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Rename files in bash

Huanfa Chen

Updates: 2022/01/22

  1. To replace all space in the file names with underscore for files of a given pattern
#!/bin/bash
for file in *.pdf *.doc; do mv "${file}" "${file// /_}"; done

Here the ${var//pattern/replacement} operator is used.

You can replace *.pdf *.doc with any pattern.

e.g., File name.pdf becomes File_name.pdf

  1. To keep the part of file name before the first occurrence of space in the file name:

e.g. 123 file name.pdf becomes 123.pdf

for file in *.pdf; do mv "${file}" "${file//\ */.pdf}"; done

Here the ${var//pattern/replacement} operator is used. It means replacing the first space and the following characters with .pdf

String operations

References: Section 34 in book ‘the Linux command line’

There is a large set of expansions that can be used to operate on strings. Many of these expansions are particularly well suited for operations on pathnames.

Removing parts of filenames

${parameter#pattern}

This expansion removes a leading portion of the shortest matched string contained in parameter defined by pattern. pattern is a wildcard pattern like those used in pathname expansion. Test code:

foo=123 file.pdf.zip
echo ${foo#*.}
#pdf.zip

${parameter##pattern}

This expansion is similar to previous one, but it removes the longest matched string.

foo=123 file.pdf.zip
echo ${foo##*.}
#zip

Replacing parts of filenames

${parameter/pattern/string}
${parameter//pattern/string}
${parameter/#pattern/string}
${parameter/%pattern/string}

This expansion performs a search-and-replace upon the contents of parameter. If text is found matching wildcard pattern, it is replaced with the contents of string. In the normal form, only the first occurrence of pattern is replaced. In the // form, all occurrences are replaced. The /# form requires that the match occur at the beginning of the string, and the /% form requires the match to occur at the end of the string. This can be used to alter the file types.

In every form, /string may be omitted, causing the text matched by pattern to be deleted.

Extract patterns from filenames

  1. To extract the pattern of 'Firstname Lastname':
ls
#two files
#'1761754 - Ma Xu abm_cw3_3314358_244875942.pdf'
#'17676 - Mi Pan ABMReport_3314358_910887307.docx'
ls | grep -oE '[[:alpha:]]+ [[:alpha:]]+'
# output
# Ma Xu
# Mi Pan
ls | grep -oE '[[:alpha:]]+ [[:alpha:]]+' > results.txt
# to output the extracted patterns into a txt file

Explanation:

grep -o means to output the extracted patterns;

grep -E means using extended regular expression grammar;

[[:alpha:]]+ means to match one or more alpha letter