bash.adoc

BASH

Table of Contents

• paths
  • Script current dir
  • get basename
• loop over files
• Arguments
• Arrays
• Split long line

paths

Script current dir

inspired from : https://www.systutorials.com/137113/how-to-get-bash-scripts-own-path/

SCRIPT_FILEPATH=$( realpath -P ${BASH_SOURCE[0]} )
SCRIPT_DIRPATH=$( dirname "${SRCIPT_FILEPATH}" )

Note	In normal Bash script, $0 is the path to the script. However, when a script is sourced, such as . a.sh`, a.sh‘s $0 does not give a.sh while the caller’s name.

or if you want to deal with bash and zsh:

if [ -z ${BASH_SOURCE+x} ]; then SCRIPT_FILEPATH=${(%):-%N};
else SCRIPT_FILEPATH=${BASH_SOURCE[0]}; fi
SCRIPT_FILEPATH=$( realpath -P ${SCRIPT_FILEPATH} )
SCRIPT_DIRPATH=$( dirname "${SCRIPT_FILEPATH}" )

get basename

$ s=/the/path/foo.txt
$ echo ${s##*/}
foo.txt
$ s=${s##*/}
$ echo ${s%.txt}
foo
$ echo ${s%.*}
foo

loop over files

for f in *.jpg
do
  convert ./"$f" ./"${f%.jpg}.pdf"
done

Arguments

	description
$0	script name as called.
$*	All parameters as single argument.
$@	All arguments, one argument per parameter.
$#	Nummber of parameters passés.
$?	Return code of last command.
$$	PID of shell running script.
$!	PID of last called processus in background.

Arrays

simple array

#!/bin/bash
array=( one two three ) # # (1)
for i in "${array[@]}" # # (2)
do
	echo $i # # (3)
done

1. defines the array values

2. loop over the values

3. access element

outputs

one
two
three

multidimensional array

#!/bin/bash
declare -A casting
casting["the narator narrator"]="edward norton"
casting["tyler durden"]="brad pit"
for actor in "${casting[@]}" ; do # # (1)
echo "with $actor"
done
for role in "${!casting[@]}" ; do # # (2)
echo "${casting[$role]} is $role"
done

1. ${casting[@]} loop over the values

2. ${!casting[@]} loop over the keys

outputs

with brad pit
with edward norton
brad pit is tyler durden
edward norton is the narator narrator

Split long line

$> cmd | cmd | cmd | cmd # some comment
$> cmd \
  | cmd \
  `# some comment` \
  | cmd \
  | cmd