Working with file extensions in bash scripts

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I’ve never been good at shell scripting. I’d much rather write scripts in a general purpose language like Python. But occasionally a shell script can do something so simply that it’s worth writing a shell script.

Sometimes a shell scripting feature is terse and cryptic precisely because it solves a common problem succinctly. One example of this is working with file extensions.

For example, maybe you have a script that takes a source file name like foo.java and needs to do something with the class file foo.class. In my case, I had a script that takes a La TeX file name and needs to create the corresponding DVI and SVG file names.

Here’s a little script to create an SVG file from a LaTeX file.

    #!/bin/bash

    latex "$1"
    dvisvgm --no-fonts "${1%.tex}.dvi" -o "${1%.tex}.svg"

The pattern ${parameter%word} is a bash shell parameter expansion that removes the shortest match to the pattern word from the expansion of parameter. So if $1 equals foo.tex, then

    ${1%.tex}

evaluates to

    foo

and so

${1%.tex}.dvi

and

${1%.tex}.svg

expand to foo.dvi and foo.svg.

You can get much fancier with shell parameter expansions if you’d like. See the documentation here.

The post Working with file extensions in bash scripts first appeared on John D. Cook.

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