All Questions
22 questions
0
votes
2
answers
789
views
Bash and other shells $(...) remove the ending newline character [duplicate]
Why the shell structure $(...) removes the ending newline character?
#!/bin/bash
S='a
b
'
printf '%i [%s]\n' "${#S}" "$S"
T=$(printf '%s' "$S")
printf '%i [%s]\n' "...
- 147
2
votes
1
answer
465
views
if var='value' then in Zsh: Is it really a valid syntax without semicolon?
The following code works on Zsh 5.8 that I tried, despite the missing semicolon. But is it really a valid Zsh syntax?
#!/bin/zsh
if var='value' then
echo 'then'
fi
Without an assignation that ...
- 147
48
votes
1
answer
13k
views
What's wrong with var=$(</dev/stdin) to read stdin into a variable?
We've seen a few posts here lately that use this:
var=$(</dev/stdin)
in an attempt to read the shell's standard input into a variable.
That is however not the correct way to do it on Linux-based ...
- 574k
7
votes
3
answers
604
views
Is there any reason to avoid sourcing the shell's configuration file?
I recently read an answer here that included the following advice:
However, as a rule, ⚠️you should not source ~/.zshrc. Depending on what's in your dotfiles, this can lead to all sorts of problems.
...
- 250k
19
votes
1
answer
2k
views
How to use associative arrays safely inside arithmetic expressions?
A few Bourne-like shells support associative arrays: ksh93 (since 1993), zsh (since 1998), bash (since 2009), though with some differences in behaviour between the 3.
A common use is for counting ...
- 574k
5
votes
3
answers
494
views
What shells support "value substitution" like MirBSD Korn Shell?
On Android (which uses mksh, MirBSD Korn Shell), there's a special syntax of string substitution (called "value substitution"):
${|commands}
Instead of collecting output of the commands (as ...
- 3,608
2
votes
2
answers
342
views
Which code works (with builtins) both in bash and zsh with the `time` keyword?
It is usual to do time cmd for many types of cmd(s) in bash:
$ time true
real 0m0.000s
user 0m0.000s
sys 0m0.000s
The output format could be changed (even to a posix format with time -p):
$...
user232326
5
votes
2
answers
2k
views
Is there a way to make the local command work portably to dash ksh bash and zsh?
In dash (and in bash zsh and some other shells) the command local works to make a variable scope limited to that function (and descendants in some cases). That enable the possibility of making a ...
user232326
21
votes
1
answer
1k
views
Is for(( ... )){ ... ;} a valid shell syntax? In which shells?
The expresion:
$ ksh -c 'for ((i=0;i<10;i++)){ echo $i;}'
0
1
2
3
4
works correctly.
I fail to find the description of this syntax in which the {...;} is replacing the ; do ...; done in the ...
user232326
14
votes
3
answers
14k
views
How to subtract two list (fast)? [duplicate]
What is a fast way to subtract two lists1. The lists may be small, maybe a direct way in shell works. Or the lists may be long, maybe external tools are the faster way.
Assume you have two lists:
...
user232326
6
votes
1
answer
1k
views
Why does CDPATH not work as documented in the manuals?
The Bourne Again shell manual says, of cd dir: […] each directory name in CDPATH is searched for dir. […] If dir begins with a slash (/), then CDPATH is not used.
The Z shell manual ...
- 71.2k
16
votes
9
answers
7k
views
Check variable is an array in Bourne like shell?
In Bourne like shell which support array variable, we can use some parsing to check if variable is an array.
All commands below were run after running a=(1 2 3).
zsh:
$ declare -p a
typeset -a a
a=(...
- 157k
6
votes
3
answers
725
views
Is "Arithmetic Expansion" the expected action on vars inside `[[` tests?
This script:
a=2
[[ "$a" -eq 2 ]] && echo yes1
[[ $a -eq 2 ]] && echo yes2
[[ a -eq 2 ]] && echo yes3
[[ "a" -eq 2 ]] && echo yes4
Does not work in dash (and ...
user79743
2
votes
2
answers
527
views
Reliably identifying the path to the directory containing the running script
There are plenty of answers in SO to address this question:
Can a Bash script tell what directory it's stored in?
Unix shell script to find out which directory the script resides?
And there are a few ...
- 42.6k
0
votes
1
answer
55
views
Is there a valid way of exporting a variable across different shells?
For some reasons, Im using ksh and zsh in my scripts and returning to -bash, I need to use already set variable values in the spawned shells, writing it to some temp file and using that didn't look ...
- 1,359