Finding Things on Linux and Understanding Regular Expressions

"There's some basic regexp-type provision built into the shell: the most basic example of this is the * wildcard. This example will list every file in the current directory which has a .jpg extension:

ls *.jpg

"What actually happens here is that the shell expands the * before it passes the file list to ls. So that line is really equivalent to

ls file1.jpg file2.jpg ...

"In contrast, this command-line will produce the same output, but using grep with full regexp syntax (see the next section for more on grep):

ls | grep '.*.jpg'

"This runs ls on the current directory (so listing all files), then passes the output through grep, which uses 'proper' regexps, rather than the shell built-in."

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