How to Batch Rename Files in a macOS Terminal?

In your specific case you can use the following bash command (bash is the default shell on macOS):

for f in *.png; do echo mv "$f" "${f/_*_/_}"; done

^{Note: If there's a chance that your filenames start with -, place -- before them[1]:
mv -- "$f" "${f/_*_/_}"}

Note: echo is prepended to mv so as to perform a dry run. Remove it to perform actual renaming.

You can run it from the command line or use it in a script.

• "${f/_*_/_}" is an application of bash parameter expansion: the (first) substring matching pattern _*_ is replaced with literal _, effectively cutting the middle token from the name.
• Note that _*_ is a pattern (a wildcard expression, as also used for globbing), not a regular expression (to learn about patterns, run man bash and search for Pattern Matching).

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If you find yourself batch-renaming files frequently, consider installing a specialized tool such as the Perl-based rename utility. On macOS you can install it using popular package manager Homebrew as follows:

brew install rename

Here's the equivalent of the command at the top using rename:

rename -n -e 's/_.*_/_/'  *.png

Again, this command performs a dry run; remove -n to perform actual renaming.

• Similar to the bash solution, s/.../.../ performs text substitution, but - unlike in bash - true regular expressions are used.

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^{[1] The purpose of special argument --, which is supported by most utilities, is to signal that subsequent arguments should be treated as operands (values), even if they look like options due to starting with -, as Jacob C. notes.}

You could use sed:

ls * | sed -e 'p;s@_.*_@_@g' | xargs -n2 mv

result:

prefix_567.png prefix_efg.png

*to do a dry-run first, replace mv at the end with echo

Explanation:

• e: optional for only 1 sed command.
• p: to print the input to sed, in this case it will be the original file name before any renaming
• @: is a replacement of / character to make sed more readable. That is, instead of using sed s/search/replace/g, use s@search@replace@g
• _.* : the underscore is an escape character to refer to the actual '.' character zero or more times (as opposed to ANY character in regex)
• -n2: indicates that there are 2 outputs that need to be passed on to mv as parameters. for each input from ls, this sed command will generate 2 output, which will then supplied to mv.

To rename files, you can use the rename utility:

brew install rename

For example, to change a search string in all filenames in current directory:

rename -nvs searchword replaceword *

Remove the 'n' parameter to apply the changes.

More info: man rename