Here is the task:
1. move all array elements to offset (index) 'off'. I.e. such, that first
array element will be at index 'off'.
2. make holes (sequences of unset elements) in the array by moving
different array parts to different offsets (indexes) off1, off2,
off3,.. .
This can't be done by
arr=( [i]="${arr[@]}" )
because "${[@]}" expansion works not as it should: it treats assignment prefix
specially, and in such case works the same as "${[*]}".
So, we should use some workaround, like
#!/bin/bash
declare -a arr=(
1
2
3
4
5
)
declare -i off=15
declare -p arr
b=${arr[0]}
unset arr[0]
arr=( [off]=$b "${arr[@]}" )
declare -p arr
This can be done simplier, but i'm not sure which version of bash this
requires
#!/bin/bash
declare -a arr=(
1
2
3
4
5
)
declare -i off=15
declare -p arr
arr=( [off]=${arr[0]} "${arr[@]:1}" )
declare -p arr
Second task can be solved like this
#!/bin/bash
declare -a arr=(
1
2
3
4
5
6
7
8
9
10
11
12
13
)
declare -i off1=15 len1=2 i1=0
declare -i off2=21 len2=3 i2=$((i1 + len1))
declare -i off3=40 len3=4 i3=$((i2 + len2))
declare -i off4=70 i4=$((i3 + len3))
declare -p arr
arr=(
[off1]=${arr[i1]} "${arr[@]:i1 + 1: len1 - 1}"
[off2]=${arr[i2]} "${arr[@]:i2 + 1: len2 - 1}"
[off3]=${arr[i3]} "${arr[@]:i3 + 1: len3 - 1}"
[off4]=${arr[i4]} "${arr[@]:i4 + 1}"
)
declare -p arr
Note, that all existed holes in the array after such operations would be lost.
четверг, 16 декабря 2010 г.
[bash] Move array elements
[bash] Write filenames to array.
Here is two general tasks:
1. Assign strings (e.g. filenames) separated by '\0' from some input
stream to corresponding array elements.
2. Convert array into stream consisting from strings separated by '\0'.
I.e we have some bash script, which somewhere get such stream, e.g. by `find`
find $root -wholename "*/$project" -prune -print0
and then we want to place this filenames into array elements. But there is a
problem: we can't use '\0' in IFS, so we can't split find's output stream
using bash word splitting expansion. And we can't use any other character to
separate filenames, because filename may contain any character.
One possible method (i don't know other, though it may be) is to transform
stream to bash code and then `eval` it.
But here is another problem: we can't simply escape string with double or
single quotes, because string may contain un-escaped double or single quotes
inside (find does not escape characters in filenames, and hence we assume,
that string contain un-escpaed characters, i.e written "as is"). For example
a"' b.txt
than after escaping with double quotes
"a"' b.txt"
or with single quotes
'a"' b.txt'
In both cases some part of string remain unescaped and not-matched quote
appears. (Write anothre example with command).
So, we can't escape string by commands like sed or awk, which perfom text
editing without string parsing. But we can use bash itself to parse and escape
string properly, and then output escaped result, like this
eval "$(find $root -wholename "*/$project" -prune -print0 \
| sort -z -s \
| xargs -0 -x bash -c '
arr=( "$@" );
declare -p arr
' escape_filename)"
(the last argument 'escape_filename' is used as $0. It may be any, but
required for correct work. For details see chapter 7.4.2 from 'info find')
Script for bash instance, invoked by xargs, may do some other operations with
strings, like
j=15;
eval "$(find $root -wholename "*/$project" -prune -print0 \
| sort -z -s \
| xargs -0 -x bash -c "
set -- \"\${@#$root/}\"
set -- \"\${@%$project}\"
arr2=( [$j]=\"\$1\" \"\${@:2}\" );
declare -p arr2
" escape_filename)"
Here we delete leading ($root) and trailing ($project) portions of filename
and then assign resulted set of strings to array starting at index $j.
Variables $root, $project and $j are substituted by main bash process before
executing pipeline.
If you use in this script array name you want assign to in main script, no
further editing of output will be needed.
Here is another example to what incorrect quoting may lead to. If we have in
input stream string like this
a' rm -rf ~ '
then quote it with single quotes and add assignment (with sed, for example)
var='a' rm -rf ~ ''
when it will be eval-ed it execute command
rm -rf ~
Here is sample script
#!/bin/bash
str="a' ls ~ '"
to_eval="$(echo "$str" | sed -e"s/^/var='/;s/$/'/")"
eval "$to_eval"
четверг, 7 октября 2010 г.
[bash][part][draft]Return values from bash function
DISCLAIMER. English language used here only for compatibility (ASCII only), so any suggestions about my bad grammar (and not only it) will be greatly appreciated.
UPD. 2010.09.07
UPD. 2010.09.07
If we need to return several values from function, we can return through
- either setting some global variables,
- or through pipe ("stdout").
- or use both.
1. Global variables.
If we do not want to hardcode these global variable names into script, we
can pass their names as arguments and then use `eval` to assign values in
child function,
f() {
..
eval "$1=\"a b\""
}
f g1
declare -p g1
but in this case there is possible name conflicts between local function's
variables and global ones. If local variable has the same name as global,
it replaces it and we no longer able to set global variable in this
child function.
2. Pipe.
If we use pipe, we'll first gather all values from local child function's
variables and send them into pipe, but then, in caller function, we'll
parse pipe content to separate these values again and assign to proper
variables. This is waste. Also, order, in which results will be outputed
into pipe, should be fixed since cutting of result into separate values
again and assigning them to proper variables into caller function assumes
certain order. And if this order sometimes accidently will change,
returned values will be messed.
f3() {
local l1='a b'
local l2=' c d'
echo "\"$l1\""
echo "\"$l2\""
return 0
}
eval "$(echo "$(f3)" | sed -e'1s/^/g1=/;2s/^/g2=/')"
declare -p g1 g2
3. Mixed.
But we can use both those techniques at the same time to eliminate all
listed above problems each of them have.
Names of global variables to be set should be passed through arguments,
but in the pipe we'll send not raw values, but assignment statements with
already expanded values, and in caller function we should simply execute
them (assignment statements) in `eval`. In such case we get:
- no name conflicts, since we're no longer need global variables into
child function: we need only their names to generate proper output,
but values to them will be assigned into `eval` in caller function.
- no parsing of pipe by caller, since child function knows names of
variables to which caller want to assign values, and send the output
with already prepared assignment statements (values in this
assignment statements must be expanded in child function, since
child's local variables will be deleted upon it returns).
- Order of variables in child function's output may be any (except,
very special cases, where one variable use the value of previous
ones), since all assignments already written and no parsing
required.
f() {
local l1='local 1'
local l2='local 2'
echo "g1=\"$l1\""
echo "g2=\"$l2\""
return 0
}
declare g1=''
declare g2=''
eval "$(f g1 g2)"
declare -p g1 g2
Note1:
- when function is called through command substitution, then it'll be
executed in the subshell (unlike, when it's called normally, it is
executed in the main shell), so you can _not_ set any parent shell's
variable inside it. Thus, all parent shell's variable, which should be
set must be written into pipe in assignment statements form.
- you can not reinitialize array in parent shell using 'arr=( ${arr[@]} )'
syntax, when writing to pipe, if array elements contain shell
'metacharacters' (not IFS characters!). This is because in `eval`-ed
script all values will be already expanded (yet before it'll be written
into pipe) and will not contain any quotes, so they'll be broken into
tokens (words and operators) by shell 'metacharacters' far before any
expansions (including word splitting by 'IFS' characters) will take
place.
- the only way to reinitialize array in parent shell is to write either
'arr[index]=value' for each element or `declare -p arr` into pipe.
Here is example.
# ./t.sh {{{
#!/bin/bash
f() {
echo "SUBSH=$BASH_SUBSHELL" >/dev/tty
arr1[3]=' g h '
arr2[3]='i k l'
IFS=" "
echo "arr1=( ${arr1[*]} )"
echo "$(declare -p arr2)"
return 0
}
declare -a arr1=(
'a b'
'c '
)
declare -a arr2=(
' d'
' e f '
)
eval "$(f)"
declare -p arr1 arr2
# }}}
Note2:
Even if we don't need any results from function, which write result into pipe,
following considerations should be looked at:
- such function should always be invoked in subshell, even if we don't
need its results. Otherwise, it'll be executed in the same shell as
parent function and its actions with FDs may result in unexpected FD
table state for parent.
- FD=1 of such function should always be connected to something like
'/dev/null'. Otherwise, it can write results somewhere you don't expect
them for.
Example-1.
Here both functions f() and f2() return result through pipe, but function f()
does not need what f2() returns, so f2() is called (before f() moves pipe)
without subshell and without pipe connected. This results in the following
problems:
- f2() closes 'fd_t_stdout' in the parent function's FD table, though f()
thinks it's still open. This resluts in "9: Bad file descriptor error",
when f() tries to move pipe and f() loses correct value for stdout.
Hence, f() writes into pipe both output intended for 'stdout' and
intended for 'pipe'.
- f2() writes its output intended for 'pipe' into the _same_ pipe, as f()
uses, because it was invoked before f() moves its own pipe.
# cat ./t.sh {{{
#!/bin/bash
declare -r -i fd_t_stdout=9
declare -r -i fd_t_pipe=7
declare -r log_file='./2.tmp'
declare -r read_file='/dev/zero'
[ -f "$log_file" ] && rm -f "$log_file"
exec 2>>"$log_file" <"$read_file"
f2() {
echo "f2(): start: \$\$: $$, BASH=$BASHPID, SUBSH=$BASH_SUBSHELL" >>"$log_file"
lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
read -rsn1
echo "f2(): move pipe" >>"$log_file"
eval "exec $fd_t_pipe>&1 1>&$fd_t_stdout-"
lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
read -rsn1
echo "f2(): write to stdout"
echo "f2(): restore pipe" >>"$log_file"
exec 1>&$fd_t_pipe-
lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
read -rsn1
echo "f2(): write to pipe"
}
f() {
echo "f(): start: \$\$: $$, BASH=$BASHPID, SUBSH=$BASH_SUBSHELL" >>"$log_file"
lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
read -rsn1
f2
echo "f(): move pipe" >>"$log_file"
eval "exec $fd_t_pipe>&1 1>&$fd_t_stdout"
lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
read -rsn1
echo "f(): write to stdout"
echo "f(): restore pipe" >>"$log_file"
eval "exec 1>&$fd_t_pipe-"
lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
read -rsn1
echo "f(): write to pipe"
}
eval "exec $fd_t_stdout>&1"
v="$(f)"
echo "v: '$v'"
eval "exec $fd_t_stdout>&-"
# }}}
# ./t.sh >|./1.tmp {{{
f(): start: $$: 12681, BASH=12683, SUBSH=1
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 12683 root 0r CHR 1,5 920 /dev/zero
t.sh 12683 root 1w FIFO 0,6 31967 pipe
t.sh 12683 root 2w REG 8,7 43 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh 12683 root 9w REG 8,7 0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
f2(): start: $$: 12681, BASH=12683, SUBSH=1
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 12683 root 0r CHR 1,5 920 /dev/zero
t.sh 12683 root 1w FIFO 0,6 31967 pipe
t.sh 12683 root 2w REG 8,7 438 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh 12683 root 9w REG 8,7 0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
f2(): move pipe
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 12683 root 0r CHR 1,5 920 /dev/zero
t.sh 12683 root 1w REG 8,7 0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
t.sh 12683 root 2w REG 8,7 805 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh 12683 root 7w FIFO 0,6 31967 pipe
f2(): restore pipe
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 12683 root 0r CHR 1,5 920 /dev/zero
t.sh 12683 root 1w FIFO 0,6 31967 pipe
t.sh 12683 root 2w REG 8,7 1175 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
f(): move pipe
./t.sh: line 36: 9: Bad file descriptor
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 12683 root 0r CHR 1,5 920 /dev/zero
t.sh 12683 root 1w FIFO 0,6 31967 pipe
t.sh 12683 root 2w REG 8,7 1492 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
f(): restore pipe
./t.sh: line 43: 7: Bad file descriptor
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 12683 root 0r CHR 1,5 920 /dev/zero
t.sh 12683 root 1w FIFO 0,6 31967 pipe
t.sh 12683 root 2w REG 8,7 1812 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
# }}}
# cat ./1.tmp {{{
f2(): write to stdout
v: 'f2(): write to pipe
f(): write to stdout
f(): write to pipe'
# }}}
Example-2.
If f() moves its pipe before calling f2(), but calls it also without subshell,
this will not be better:
- f2() will write its output intended for 'pipe' into 'stdout', since
stdout instead of pipe will be opened at FD=1, when f2() starts.
- f2() replaces FD='fd_t_pipe' value into parent function's FD table, so
saved f()'s pipe will be replaced with 'stdout' (since 'stdout' will be
at FD=1 in f2()). So, f() loses correct value for its pipe and writes
into 'stdout' both output intended for pipe and intended for 'stdout'.
# cat ./t.sh {{{
#!/bin/bash
declare -r -i fd_t_stdout=9
declare -r -i fd_t_pipe=7
declare -r log_file='./2.tmp'
declare -r read_file='/dev/zero'
[ -f "$log_file" ] && rm -f "$log_file"
exec 2>>"$log_file" <"$read_file"
f2() {
echo "f2(): start: \$\$: $$, BASH=$BASHPID, SUBSH=$BASH_SUBSHELL" >>"$log_file"
lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
read -rsn1
echo "f2(): move pipe" >>"$log_file"
eval "exec $fd_t_pipe>&1 1>&$fd_t_stdout-"
lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
read -rsn1
echo "f2(): write to stdout"
echo "f2(): restore pipe" >>"$log_file"
exec 1>&$fd_t_pipe-
lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
read -rsn1
echo "f2(): write to pipe"
}
f() {
echo "f(): start: \$\$: $$, BASH=$BASHPID, SUBSH=$BASH_SUBSHELL" >>"$log_file"
lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
read -rsn1
echo "f(): move pipe" >>"$log_file"
eval "exec $fd_t_pipe>&1 1>&$fd_t_stdout"
lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
read -rsn1
f2
echo "f(): write to stdout"
echo "f(): restore pipe" >>"$log_file"
eval "exec 1>&$fd_t_pipe-"
lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
read -rsn1
echo "f(): write to pipe"
}
eval "exec $fd_t_stdout>&1"
v="$(f)"
echo "v: '$v'"
eval "exec $fd_t_stdout>&-"
# }}}
# ./t.sh >|./1.tmp {{{
f(): start: $$: 12713, BASH=12715, SUBSH=1
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 12715 root 0r CHR 1,5 920 /dev/zero
t.sh 12715 root 1w FIFO 0,6 32160 pipe
t.sh 12715 root 2w REG 8,7 43 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh 12715 root 9w REG 8,7 0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
f(): move pipe
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 12715 root 0r CHR 1,5 920 /dev/zero
t.sh 12715 root 1w REG 8,7 0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
t.sh 12715 root 2w REG 8,7 409 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh 12715 root 7w FIFO 0,6 32160 pipe
t.sh 12715 root 9w REG 8,7 0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
f2(): start: $$: 12713, BASH=12715, SUBSH=1
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 12715 root 0r CHR 1,5 920 /dev/zero
t.sh 12715 root 1w REG 8,7 0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
t.sh 12715 root 2w REG 8,7 893 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh 12715 root 7w FIFO 0,6 32160 pipe
t.sh 12715 root 9w REG 8,7 0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
f2(): move pipe
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 12715 root 0r CHR 1,5 920 /dev/zero
t.sh 12715 root 1w REG 8,7 0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
t.sh 12715 root 2w REG 8,7 1349 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh 12715 root 7w REG 8,7 0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
f2(): restore pipe
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 12715 root 0r CHR 1,5 920 /dev/zero
t.sh 12715 root 1w REG 8,7 22 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
t.sh 12715 root 2w REG 8,7 1752 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
f(): restore pipe
./t.sh: line 43: 7: Bad file descriptor
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 12715 root 0r CHR 1,5 920 /dev/zero
t.sh 12715 root 1w REG 8,7 63 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
t.sh 12715 root 2w REG 8,7 2105 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
# }}}
# cat ./1.tmp {{{
f2(): write to stdout
f2(): write to pipe
f(): write to stdout
f(): write to pipe
v: ''
# }}}
Example-3.
And here is how this can be done correctly. Shortly, we should call f2() like
( f2 >/dev/null )
In this case, f2() result will be discarded (but we do not need it, right?), but
f() will output its result as expected.
# cat ./t.sh {{{
#!/bin/bash
declare -r -i fd_t_stdout=9
declare -r -i fd_t_pipe=7
declare -r log_file='./2.tmp'
declare -r read_file='/dev/zero'
[ -f "$log_file" ] && rm -f "$log_file"
exec 2>>"$log_file" <"$read_file"
f2() {
echo "f2(): start: \$\$: $$, BASH=$BASHPID, SUBSH=$BASH_SUBSHELL" >>"$log_file"
lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
read -rsn1
echo "f2(): move pipe" >>"$log_file"
eval "exec $fd_t_pipe>&1 1>&$fd_t_stdout-"
lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
read -rsn1
echo "f2(): write to stdout"
echo "f2(): restore pipe" >>"$log_file"
exec 1>&$fd_t_pipe-
lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
read -rsn1
echo "f2(): write to pipe"
}
f() {
echo "f(): start: \$\$: $$, BASH=$BASHPID, SUBSH=$BASH_SUBSHELL" >>"$log_file"
lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
read -rsn1
echo "f(): move pipe" >>"$log_file"
eval "exec $fd_t_pipe>&1 1>&$fd_t_stdout"
lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
read -rsn1
( f2 >/dev/null )
echo "f(): write to stdout"
echo "f(): restore pipe" >>"$log_file"
eval "exec 1>&$fd_t_pipe-"
lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
read -rsn1
echo "f(): write to pipe"
}
eval "exec $fd_t_stdout>&1"
v="$(f)"
echo "v: '$v'"
eval "exec $fd_t_stdout>&-"
# }}}
# ./t.sh >|./1.tmp {{{
f(): start: $$: 12777, BASH=12779, SUBSH=1
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 12779 root 0r CHR 1,5 920 /dev/zero
t.sh 12779 root 1w FIFO 0,6 32627 pipe
t.sh 12779 root 2w REG 8,7 43 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh 12779 root 9w REG 8,7 0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
f(): move pipe
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 12779 root 0r CHR 1,5 920 /dev/zero
t.sh 12779 root 1w REG 8,7 0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
t.sh 12779 root 2w REG 8,7 409 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh 12779 root 7w FIFO 0,6 32627 pipe
t.sh 12779 root 9w REG 8,7 0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
f2(): start: $$: 12777, BASH=12784, SUBSH=2
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 12784 root 0r CHR 1,5 920 /dev/zero
t.sh 12784 root 1w CHR 1,3 898 /dev/null
t.sh 12784 root 2w REG 8,7 893 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh 12784 root 7w FIFO 0,6 32627 pipe
t.sh 12784 root 9w REG 8,7 0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
t.sh 12784 root 10w REG 8,7 0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
f2(): move pipe
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 12784 root 0r CHR 1,5 920 /dev/zero
t.sh 12784 root 1w REG 8,7 0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
t.sh 12784 root 2w REG 8,7 1410 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh 12784 root 7w CHR 1,3 898 /dev/null
t.sh 12784 root 10w REG 8,7 0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
f2(): restore pipe
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 12784 root 0r CHR 1,5 920 /dev/zero
t.sh 12784 root 1w CHR 1,3 898 /dev/null
t.sh 12784 root 2w REG 8,7 1874 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh 12784 root 10w REG 8,7 22 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
f(): restore pipe
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 12779 root 0r CHR 1,5 920 /dev/zero
t.sh 12779 root 1w FIFO 0,6 32627 pipe
t.sh 12779 root 2w REG 8,7 2248 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh 12779 root 9w REG 8,7 43 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
# }}}
# cat ./1.tmp {{{
f2(): write to stdout
f(): write to stdout
v: 'f(): write to pipe'
# }}}
четверг, 30 сентября 2010 г.
[draft][part] Shell I/O redirection
DISCLAIMER. English language used here only for compatibility (ASCII only), so any suggestions about my bad grammar (and not only it) will be greatly appreciated.
1. Open file descriptors table maps number (file descriptor - FD) into actual
file to which output will be written.
+----+------------+
| FD | File |
+----+------------+
| 0 | /dev/vc/1 |
+----+------------+
| 1 | /dev/vc/1 |
+----+------------+
| 2 | /dev/vc/1 |
+----+------------+
| ... |
2. Redirection operators (shell) affect (change) only 'File' column of the
table. So, if program writes to FD=5 (write(5,..); call) you can _not_
force it to write to another FD with shell redirection - you can only
change the content of 'File' column in the FD=5 row (i.e to what file FD=5
is mapped) and through that change to where output arrives at the end (to
which file).
3. '/dev/stdout' and '/dev/stderr' are _not_ an actual files, they're _links_
to what is _now_ opened at FD=1 and FD=2 correspondingly. I.e links to
file specified in 'File' column of FD=1 and FD=2 rows.
# ls -l /dev/stdout /dev/stderr
lrwxrwxrwx 1 root root 15 Sep 30 07:56 /dev/stderr -> /proc/self/fd/2
lrwxrwxrwx 1 root root 15 Sep 30 07:56 /dev/stdout -> /proc/self/fd/1
4. In construction like
f() {
echo "abc"
return 0
}
res=$(f)
function f() result are sent through pipe to the caller. I think, this is
not clear to say, that result are sent through "stdout", though it's
correct, since "stdout" is _not_ an actual file - it's a link to what is
now opened at file descriptor 1, and now there will be pipe. By default,
when function invoked through command substitution (function will be
executed in a subshell), pipe is opened for writing at FD=1 for child
process (function) and for reading at FD=3 for caller process. So, if you
use something like
echo "abc"
"abc" will be written into pipe (because `echo` always writes to FD=1). But
if you want, that the way how we send result does not affect function's
code, we should move 'pipe' from FD=1 into some unused FD and restore
original FD=1 content.
exec 7>&1 1>&2
When result will be ready, we move 'pipe' back to FD=1 and `echo` result
into it.
exec 1>&7-
echo "result"
Note, that for all child subshells pipe will be opened as well.
Example. Illustrates complete implementation, with several stacked functions
returning result through pipe.
#!/bin/bash
log='./t.log'
read_f='/dev/null'
rm -f $log
f2() {
echo "f2(): SUBSH=$BASH_SUBSHELL" >>$log
echo "f2(): BASHPID[$BASHPID]:" >>$log
lsof -a -p $BASHPID -d '^mem,^cwd,^rtd,^txt' >>$log
echo "f2(): stdout-1: ghi"
echo "f2(): stderr-1: klm" >/dev/stderr
echo "f2(): Before moving pipe somewhere" >>$log && read -n1 < $read_f
eval "exec $save_pipe>&1 1>&$save_stdout-"
echo "f2(): BASHPID[$BASHPID]:" >>$log
lsof -a -p $BASHPID -d '^mem,^cwd,^rtd,^txt' >>$log
echo "f2(): stdout-2: ghi"
echo "f2(): stderr-2: klm" >/dev/stderr
echo "f2(): Before exit f2()" >>$log && read -n1 < $read_f
return 0
}
f() {
echo "f(): SUBSH=$BASH_SUBSHELL" >>$log
echo "f(): \$\$[$$]:" >>$log
lsof -a -p $$ -d '^mem,^cwd,^rtd,^txt' >>$log
echo "f(): BASHPID[$BASHPID]:" >>$log
lsof -a -p $BASHPID -d '^mem,^cwd,^rtd,^txt' >>$log
echo 'f(): stdout-1: abc'
echo 'f(): stderr-1: def' >/dev/stderr
echo "f(): Before moving pipe somewhere" >>$log && read -n1 < $read_f
eval "exec $save_pipe>&1 1>&$save_stdout-"
echo "f(): BASHPID[$BASHPID]:" >>$log
lsof -a -p $BASHPID -d '^mem,^cwd,^rtd,^txt' >>$log
echo 'f(): stdout-2: abc'
echo 'f(): stderr-2: def' >/dev/stderr
echo "f(): Before calling f2()" >>$log && read -n1 < $read_f
eval "exec $save_stdout>&1"
v=$(f2)
echo "-$v-"
eval "exec $save_stdout>&-"
echo "f(): BASHPID[$BASHPID]:" >>$log
lsof -a -p $BASHPID -d '^mem,^cwd,^rtd,^txt' >>$log
echo "f(): Before restoring pipe" >>$log && read -n1 < $read_f
exec >&$save_pipe-
echo 'f(): stdout-3: abc'
echo 'f(): stderr-3: def' >/dev/stderr
echo "f(): BASHPID[$BASHPID]:" >>$log
lsof -a -p $BASHPID -d '^mem,^cwd,^rtd,^txt' >>$log
echo "f(): Before exit f()" >>$log && read -n1 < $read_f
return 0
}
declare -r -i save_stdout=9
declare -r -i save_pipe=7
eval "exec $save_stdout>&1"
v=$(f)
eval "exec $save_stdout>&-"
echo "in main()"
echo "\$\$[$$]:" >>$log
lsof -a -p $$ -d '^mem,^cwd,^rtd,^txt' >>$log
echo "-$v-"
Here is illustration:
(subshell)
main() ....................
+--------------+ . f() .
| 3r pipe | call f() . +--------------+ .
| 9u "stdout" |----------->| 1w pipe(f) | .
+--------------+ . | 9u "stdout" | .
. +--------------+ .
. | .
. | move pipe(f)
. | .
. v . (subshell)
. +--------------+ . ....................
. | 1w "stdout" | . . f2() .
. | 7w pipe(f) | call f2() . +--------------+ .
. | 9- (closed) |------------>| 1w pipe(f2) | .
. +--------------+ . . | 7w pipe(f) | .
. . . | 9u "stdout" | .
. . . +--------------+ .
. . . | .
. . . | move pipe(f2)
. . . | over pipe(f)
. . . | .
. . . v .
. . . +--------------+ .
. +--------------+ . return . | 1w "stdout" | .
. | 1w "stdout" |<------------| 7w pipe(f2) | .
. | 7w pipe(f) | . . | 9- (closed) | .
. +--------------+ . . +--------------+ .
. | . ....................
. | restore pipe(f)
. | .
. v .
. +--------------+ .
+--------------+ return . | 1w pipe(f) | .
| 1u "stdout" |------------| 7- (closed) | .
+--------------+ . +--------------+ .
....................
And here is log (slightly edited)
# ./t.sh >|./1.tmp
f(): SUBSH=1
f(): $$[4794]:
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 4794 root 0u CHR 4,1 5466 /dev/vc/1
t.sh 4794 root 1w REG 8,7 0 1121662 .../1.tmp
t.sh 4794 root 2u CHR 4,1 5466 /dev/vc/1
t.sh 4794 root 3r FIFO 0,6 14132 pipe
t.sh 4794 root 9w REG 8,7 0 1121662 .../1.tmp
t.sh 4794 root 255r REG 8,7 2075 1121653 .../t.sh
f(): BASHPID[4796]:
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 4796 root 0u CHR 4,1 5466 /dev/vc/1
t.sh 4796 root 1w FIFO 0,6 14132 pipe
t.sh 4796 root 2u CHR 4,1 5466 /dev/vc/1
t.sh 4796 root 9w REG 8,7 0 1121662 .../1.tmp
f(): Before moving pipe somewhere
f(): BASHPID[4796]:
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 4796 root 0u CHR 4,1 5466 /dev/vc/1
t.sh 4796 root 1w REG 8,7 0 1121662 .../1.tmp
t.sh 4796 root 2u CHR 4,1 5466 /dev/vc/1
t.sh 4796 root 7w FIFO 0,6 14132 pipe
f(): Before calling f2()
f2(): SUBSH=2
f2(): BASHPID[4803]:
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 4803 root 0u CHR 4,1 5466 /dev/vc/1
t.sh 4803 root 1w FIFO 0,6 14194 pipe
t.sh 4803 root 2u CHR 4,1 5466 /dev/vc/1
t.sh 4803 root 7w FIFO 0,6 14132 pipe
t.sh 4803 root 9w REG 8,7 19 1121662 .../1.tmp
f2(): Before moving pipe somewhere
f2(): BASHPID[4803]:
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 4803 root 0u CHR 4,1 5466 /dev/vc/1
t.sh 4803 root 1w REG 8,7 19 1121662 .../1.tmp
t.sh 4803 root 2u CHR 4,1 5466 /dev/vc/1
t.sh 4803 root 7w FIFO 0,6 14194 pipe
f2(): Before exit f2()
f(): BASHPID[4796]:
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 4796 root 0u CHR 4,1 5466 /dev/vc/1
t.sh 4796 root 1w REG 8,7 61 1121662 .../1.tmp
t.sh 4796 root 2u CHR 4,1 5466 /dev/vc/1
t.sh 4796 root 7w FIFO 0,6 14132 pipe
f(): Before restoring pipe
f(): BASHPID[4796]:
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 4796 root 0u CHR 4,1 5466 /dev/vc/1
t.sh 4796 root 1w FIFO 0,6 14132 pipe
t.sh 4796 root 2u CHR 4,1 5466 /dev/vc/1
f(): Before exit f()
$$[4794]:
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
t.sh 4794 root 0u CHR 4,1 5466 /dev/vc/1
t.sh 4794 root 1w REG 8,7 71 1121662 .../1.tmp
t.sh 4794 root 2u CHR 4,1 5466 /dev/vc/1
t.sh 4794 root 255r REG 8,7 2075 1121653 .../t.sh
четверг, 20 мая 2010 г.
[summary][draft][part] Tabs in vim
DISCLAIMER. English language used here only for compatibility (ASCII only), so any suggestions about my bad grammar (and not only it) will be greatly appreciated.
Status: summary.
State: draft,part.
Detailed description: Some tables for illustrate <Tab>'s handling in vim. See vim help for details.
Status: summary.
State: draft,part.
Detailed description: Some tables for illustrate <Tab>'s handling in vim. See vim help for details.
Tabs in vim {{{
'sts' and 'sta' options {{{
Following options affect <Tab>s and indents:
'tabstop' 'ts'
'shiftwidth' 'sw'
'softtabstop' 'sts'
'smarttab' 'sta'
'expandtab' 'et'
'sw' and 'ts' define standard vim operations behavior, they are not
switches for some features (hence they're always set and always used).
But 'sts' and 'sta' enables additional features, which affect (change)
some vim operations behavior (hence, they can be unset to turn feature
off).
Table below shows what option will be used to determine how many
positions insert or delete during some editing operations depending on
activated modes: both 'sts' and 'sta' are off (default), 'sts' set,
'sta' set and both 'sts' and 'sta' set. When editing operation insert
less (or more) positions, than real <Tab> counts for, mix from spaces
and real <Tab>s are used.
+--------------------------+-------------------------------------------+
| Operation | Will be inserted .. positions |
| +------+-----------+-----------+------------+
| | | +sts | +sta | +sts +sta |
+--------------------------+------+-----------+-----------+------------+
| Use >> , etc | sw | sw | sw | sw |
+--------------------------+------+-----------+-----------+------------+
| Type <Tab> or <BS> | ts | sts (mix) | | |
| + + +-----------+------------+
| at the start of line | | | sw (mix) | sw (mix) |
| + + +-----------+------------+
| in other places | | | ts | sts (mix) |
+--------------------------+------+-----------+-----------+------------+
| Real <Tab> length | ts | ts | ts | ts |
+--------------------------+------+-----------+-----------+------------+
}}}
':retab' and changing 'ts' option value {{{
'ts' option changes real tabstop, but does not change text. Hence,
indents, which made according to old tabstop, probably will be messed
(i.e there will be visible changes in text), but actual file remains
untouched. So, using 'undo' after changing 'ts' has no sense.
:retab command changes both 'ts' option and text according to new 'ts'
value in such way, that all indents remain the same (there will be no
visible changes), though actual file will be changed (to preserve
visible indents :retab pads them, if necessary, with spaces). So,
using 'undo' after :retab recover text to previous state, but not
recover 'ts' to previous value, hence indents may be messed (like
after you change only 'ts') and to recover visible text state you need
set 'ts' to previous value. Table below summarizes that.
+-------------------+---------------+-----------+
| | Change 'ts' | :retab |
+-------------------+---------------+-----------+
| 'ts' changed? | yes | yes |
+-------------------+---------------+-----------+
| File changed? | no | yes |
+-------------------+---------------+-----------+
| Visible changes? | yes | no |
+-------------------+---------------+-----------+
}}}
}}}
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