Bash cheatsheet

admin

14:15:55, 19 May 2023

Find port in nginx configs recursively

grep 8080 --include='*.conf' -r /etc/nginx

sed dry-run

sed 's/Dimensions/Габариты/' /tmp/woocommerce-ru_RU.po | less

Print files directories with hidden (.dot-started)

nkonev@localhost ~ $ find `pwd` -mindepth 1 -maxdepth 1

/home/nkonev/Programming

/home/nkonev/Общедоступные

/home/nkonev/.ssh

/home/nkonev/.cache

Print all arguments passed to all java processes

for j in `pgrep java`; do

cat /proc/${j}/cmdline | tr '\0' ' '

echo

done

Float-pointed calculations

nkonev@localhost ~ $ echo '3.0 / 2' | bc -l

1.50000000000000000000

Literature

Advanced Bash-Scripting Guide

Bash Reference Manual

---

Linux console terminal

admin at 14:19:03, 19 May 2023

Logging in Bash or redirect stdout & stderr to syslog

#!/bin/bash

exec 1> >(logger -s -t "$(basename $0) stdout")

exec 2> >(logger -s -t "$(basename $0) stderr")

echo Starting dumping databases

echo Error >&2

Inspired by https://urbanautomaton.com/blog/2014/09/09/redirecting-bash-script-output-to-syslog/

https://habr.com/post/281601/

admin at 14:21:28, 19 May 2023

Piping stdout & stderr to different terminals

Separating stdout & stderr between terminals in bash

su -

mkfifo /tmp/ping-out

mkfifo /tmp/ping-err

exec 3<>/tmp/ping-out

exec 4<>/tmp/ping-err

strace ping ya.ru 2>&4 >&3

in another terminal

cat /tmp/ping-out

in another terminal

cat /tmp/ping-err

less -f /tmp/ping-err

then press Shift+F

Inspired from http://tldp.org/LDP/abs/html/system.html

Piping stderr of strace to less

strace df 2>&1 >/dev/null | less

Debugging ping

su -

strace ping ya.ru 2>&1 >/dev/null | less

Press Shift+F

admin at 14:23:21, 19 May 2023

Find out broken symlinks

# Find

find /usr/bin | xargs file | grep broken

# Remove it

sudo find -L /usr/bin/* -name . -o -type d -prune -o -type l -exec rm {} +

admin at 14:25:17, 19 May 2023

Launch app detached (daemonized)

Option 1 Stack Overflow

nohup nautilus > /dev/null &

Option 2 felixmilea.com

vim $HOME/bin/ds

insert

#!/bin/sh

if test -t 1; then

exec 1>/dev/null

fi

if test -t 2; then

exec 2>/dev/null

fi

"$@" &

Make executable

chmod +x $HOME/bin/ds

Try it:

ds nautilus

admin at 14:26:27, 19 May 2023

Debug bash script

For interactive debug - add debug trap;

Or, if you just want see execution verbosely do export PS4 & set -x

#!/bin/bash

trap '(read -p "[$BASH_SOURCE:$LINENO] $BASH_COMMAND?")' DEBUG

export PS4='# ${BASH_SOURCE}:${LINENO}: ${FUNCNAME[0]}() - [${SHLVL},${BASH_SUBSHELL},$?] '

set -e

set -x

VAR=ololo

for ((i = 0; i<10; ++i)); do

echo iteration $i $VAR

done

echo Goodbye

Links

http://tldp.org/LDP/abs/html/internalvariables.html

http://www.skybert.net/bash/debugging-bash-scripts-on-the-command-line/

http://www.softpanorama.org/Scripting/Shellorama/bash_debugging.shtml

http://wiki.bash-hackers.org/scripting/debuggingtips

http://bashdb.sourceforge.net/ - external bash debugger

-nvxeu (https://www.tldp.org/LDP/abs/html/debugging.html, https://www.tldp.org/LDP/abs/html/options.html)

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