Bash String Substitution

bash_string_substitution.md

Syntax

${varName/Pattern/Replacement}

Given a variable

$ val="test"

Replace first occurence/match

$ echo "${val/t/T}"
Test

Replace all occurences/matches

$ echo "${val//t/T}"
TesT

This can be applied to file input, e.g., replace a comma with a semicolon (a on-liner)

$ echo "a1,b2,c3" > eg.csv
$ while read line; do echo "${line//','/$'\t'}" >> eg.tsv; done < eg.csv
$ cat eg.tsv
a1	b2	c3

Note:

• The tab needs to be escaped as $'\t', which is a quoted string-expansion construct
• Same applies to others like newlines

Refrence:

• HowTo: Use Bash Parameter Substitution Like A Pro