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[onceupon]

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[Bushmills]

As there's no section dealing with brace expansion, here's a useful example which can reduce typos and save keystrokes:

mv long_and_complicated_filename.{foo,bar}

This, when executed, expands to:

mv long_and_complicated_filename.foo long_and_complicated_filename.bar

[mu578]

In that case it is named filename expansion. I think the default mode today is ERE (Extended Regular Expression, to handle more complex glob patterns, space, unicodes etc).

see:

• glob patterns
• brace expansion
• filename expansion
• learn awk

touch filename[0-9]   // existing files
touch filename{0..9} // create files

[Bushmills]

Frequently one wished to place nicely formatted headers into output, consisting of a line of specific chars, then a line of output, and another line of specific chars, those with the same length as the output line. That can be done like this:

line="foo bar"; printf "%s\n%s\n%s\n" "${line//?/=}" "$line" "${line//?/=}"

"line" may of course be passed as argument, when writing the above code as function. Also, header can be customised, for example with leading/trailing "#" chars according personal taste and need. Idea here is merely to generate header bracketing lines with the same length as the header line itself, by replacing all of its characters against the desired header character.

With leading "#" chars the line could look like this:
line="foo bar"; printf "# %s\n# %s\n# %s\n" "${line//?/=}" "$line" "${line//?/=}"