grep is the name of a common utility on many Unix or unix like
systems.

Folklore says that the name represents a command that developers
''in the old days'' used to issue within their editor or other
similar program:

   g/re/p

which was a ''global {regular expression} print'' command.

Grep reads through one or more input streams (stdin or files),
searching for a string of text which represents some for of a [regular expression],
and, depending on options provided, may produce the matching
lines of input.
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[RS] wrote this tiny, and feature-poor, emulation for use on [PocketPC] (but it should run elsewhere too):
 proc grep {re args} {
    set files [eval glob -types f $args]
    foreach file $files {
       set fp [open $file]
       while {[gets $fp line] >= 0} {
          if [regexp -- $re $line] {
             if {[llength $files] > 1} {puts -nonewline $file:}
             puts $line
           }
       }
       close $fp
    }
 }


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see also [a grep-like utility]

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[category application]