19
votes
This 'while' loop countdown with sleep doesn't work
SECONDS is a variable that's used internally by Bash, and the way this variable works is interfering with your script's decrement action. If you use a different variable name (like SECS or seconds) ...
- 3,963
17
votes
Accepted
Can a script be run as a subshell?
(. ./myscript.sh)
is the right way (the standard form is ., not source, and . with no directory specified searches on the PATH).
Doing this using a shebang would require having a reliable way of ...
- 423k
14
votes
Accepted
Looking for a more permissive alternative to GNU getopt for wrapper script
A common method for tasks like this is to use -- as a separator between options to be handled by the wrapper script and options to be passed on verbatim to the program being executed by the wrapper, e....
- 77.7k
10
votes
This 'while' loop countdown with sleep doesn't work
As @SottoVoce said, $SECONDS is a special variable in bash and other Korn-like shells.
In bash and ksh (not zsh), unsetting the variable as with unset -v SECONDS removes its special meaning, but in ...
- 533k
10
votes
Accepted
Update crontab rules without overwriting or duplicating
From what I can tell, there's no way to tell crontab to refer to a set of files to collate the rules (without duplication or overwriting)/
There is, but not for user crontabs. Use individual files in ...
- 71.3k
7
votes
Accepted
Feed function specific files from the directory
#!/bin/sh
set -- *_file.txt
until [ "$#" -lt 2 ]; do
process "$1" "$2" >"output_${1%_file.txt}${2%_file.txt}"
shift 2
done
This sets the ...
- 327k
7
votes
Feed function specific files from the directory
You could do this with the xargs command. If I have these files:
$ ls
A_file.txt B_file.txt C_file.txt D_file.txt E_file.txt F_file.txt G_file.txt H_file.txt
Then I can process these two at a ...
- 33.2k
7
votes
Sed based on 2 words, then replace whole line with variable
To let the c command only affect lines that contain both banana and wait, make sure to skip all lines that don't match these two patterns. You may do this using the b command, which will branch to ...
- 327k
7
votes
Accepted
Race condition not seen while two scripts write to a same file
Simply, the echo command triggers one write syscall which is atomic.
Note that write doesn’t guarantee to write all bytes it is given, but in this case (few data), it does.
Then in theory write(fd, ...
- 2,613
6
votes
AWK reading path from text file
You could build the same logic with the print/no-print flag inside the while(getline) loop. Something like this:
awk '{ while((getline a < $0) > 0) {
if (a ~ /BEGIN/) p=1;
if (p) print ...
- 135k
6
votes
Accepted
SSH session termination on script error when sourcing multiple sub-scripts
The reason this is happening is because you are sourcing the master script. I can reproduce the behavior you describe using these two toy examples:
terdon@oregano ~ $ cat ~/scripts/foo.sh
#!/bin/bash
...
- 239k
5
votes
Feed function specific files from the directory
If switching from bash to zsh is an option, then it's just:
for i j ( *.txt(N) ) some_program -- $i $j > output_$i[1]$j[1]
(N) enables nullglob from that one glob expansion so as not to report an ...
- 533k
5
votes
How to extract part of URL from curl response in bash script?
With GNU grep:
$ grep -oP 'https://[^/]+/\d+/\K.*' <<< 'https://www.example.com/1234/text/111?x=999988'
text/111?x=999988
Or
With Perl:
$ perl -nE 'say $& if m@https://[^/]+/\d+/\K.*@' &...
- 32.7k
5
votes
Accepted
How to pass string from bash to python function
Make it a shell function instead. Paste this into your terminal, or add to your shell's configuration files (e.g. ~/.bashrc for bash)
pipeline_test(){
python -c 'from sys import argv; from ...
- 239k
5
votes
Accepted
Is it a good idea to put "export BASH_ENV=~/.bashrc" in my .bashrc?
IMO, no it's not a good idea.
You'd be better off explicitly sourcing your library of functions and variables (aliases don't work in non-interactive shells unless the expand_aliases shell option is ...
- 77.7k
5
votes
Accepted
How to make the (N) patterns of the zsh eatable by bash?
From zsh_expn:
N sets the NULL_GLOB option for the current pattern
So, the bash way would be to set the nullglob option for that pattern.
( shopt -s nullglob || setopt NULL_GLOB && ...
- 25.2k
4
votes
Problem with getting unique output in script
If you have GNU grep, the default on Linux, you could simplify with :
extract_parts(){
grep -oP 'https?://\K[^/]+' "$1" | sort -u
}
Output
$ extract_parts wget-list
downloads....
- 32.7k
4
votes
what are practical uses of stdbuf or nohup?
Let's start with an example without stdbuf. You need 2 terminals because tail -f will block.
Terminal 1
touch log_file1
tail -f log_file1 | cut -d " " -f 1 | uniq
Terminal 2
echo "A 1&...
- 151
4
votes
Accepted
Problem with getting unique output in script
while read a; do
You're reading one line...
host=$(echo -e "$a" | awk -F '/' '{print $1}' | sort -u)
and printing that in a pipeline which you then sort and take the unique lines out of. ...
- 135k
4
votes
AWK reading path from text file
Something like the following, untested, will do what you want using any awk:
awk '
NR == FNR { ARGV[ARGC++]=$0; next }
$1 == "BEGIN" { f=1 }
f
$0 == "END BEGIN" { f=...
- 30.2k
4
votes
Shell script: How to prepend env variable with prefix only if environment variable is defined?
command ${VALUE:+--flag "$VALUE"}
This runs command with the option --flag and its option-argument "$VALUE" if the variable VALUE is defined and non-empty. If the variable is ...
- 327k
4
votes
Accepted
How to make my script stay executable on different devices?
When I copy the script to a flash drive and then copy it from a flash drive to another computer running the same operating system I have to make it executable again to give back the function to right ...
- 526
4
votes
Update crontab rules without overwriting or duplicating
You can use serie of command to accomplish this. Here is sample script to do it:
#get current cron
crontab -l >cron_c
#add new lines
echo "0 * * * * command" >>cron_c
#remove ...
- 17.2k
4
votes
How to make the (N) patterns of the zsh eatable by bash?
If it's in a zsh-specific part, you can avoid bash complaining upon parsing that code that it will never run by doing:
eval 'cmd this_pattern*(N)'
instead of
cmd this_pattern*(N)
That eval command ...
- 533k
4
votes
Accepted
How and why does using redirection or writing files within an if statement affect exit code?
$?
In the PARAMETERS SET BY THE SHELL section of man zshparam, or info zsh 'Parameters Set By The Shell' you'll see that, $? is the exit status returned by the last command.
$(...)
In man zshexpn or ...
- 4,025
4
votes
How to improve script for redacting and copying a file
First off, always quote your variables and this goes double if they store file names, since they can have any character except NUL (\0) and /. You're also doing some unnecessary movement and creation ...
- 239k
3
votes
While working on a file in a gui application, how to quickly open the parent directory of a file in the file browser?
Please check Open File Explorer on a File that is open by another Application. I am the OP of that question. menu's answer is the accepted one. Here is the complete solution. However, to understand ...
- 2,560
3
votes
How do I resolve a relative path in a POSIX shell if readlink/realpath is not available?
There is a realpath C function, though. So maybe one of the other utilities uses it secretly?
From the top of my head, I'm not aware any of those utilities reference the realpath function in their ...
- 431
3
votes
Accepted
how to interpret service command output
Instead of looking at the output, you should check service’s exit code:
if service apparmor status >&/dev/null; then echo AppArmor is loaded and enabled; fi
This needs to run as root to ...
- 423k
3
votes
Can a script be run as a subshell?
POSIX (IEEE Std 1003.1-2017, Section 2.12) specifies:
A subshell environment shall be created as a duplicate of the shell environment, except that signal traps that are not being ignored shall be set ...
- 190
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