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UNIX Commands RTFM: grep(1), egrep(1) & fgrep(1)

UNIX Commands RTFM: grep(1), egrep(1) & fgrep(1). Gilbert Detillieux April 13, 2010 MUUG Meeting. What’s in a name?. grep : g lobal r egular e xpression p rint Comes from UNIX editor command: g/ re /p egrep : extended grep Extended (or full ) regular expressions

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UNIX Commands RTFM: grep(1), egrep(1) & fgrep(1)

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  1. UNIX CommandsRTFM: grep(1), egrep(1) & fgrep(1) Gilbert Detillieux April 13, 2010MUUG Meeting

  2. What’s in a name?... • grep: global regular expression print • Comes from UNIX editor command: g/re/p • egrep: extendedgrep • Extended (or full) regular expressions • fgrep: fastgrep or fixed-string grep • Matches fixed or literal strings • Historically, much faster than grep/egrep

  3. Limited Regular Expressions • A.k.a. “basic” regular expressions • Alpha-numerics match literally • So does some punctuation, unless special • Similar to wildcards in file-name “globbing” • “.” matches any single character • “*” matches any number of previous character(including zero) • Use “\.” (or “\*”) to match thosespecial characters literally

  4. Limited Regular Expressions (cont.) • Character classes: • “[0-9]” matches any digit • “[^A-Za-z]” matches anything but letters • “[0-9-]” matches “-” (literally) or a digit • “[][]” matches “]” or “[” (literally) • Anchors: • “^” matches beginning of line: “^From” • “$” matches end of line: “*$”

  5. Full Regular Expressions • A.k.a. “extended” regular expressions • Additional repetition operators like “*”… • “?” matches zero or one instance of previous character or sub-expression • “+” matches one or more instances of previous character or sub-expression

  6. Full Regular Expressions (cont.) • Sub-expressions enclosed in “(…)”: • “(the)?end” matches “end” or “the end” • “(pretty)*please” • Alternatives separated by “|”… • “(this|that|theother)” • “(this|that|)” • And many more extensions (possibly)…

  7. grep(1) Man Page • NAME • grep, egrep, fgrep – print lines matching a pattern • SYNOPSIS • grep [-cilnqv]... PATTERN [ FILE … ] • grep [-cilnqv]... [ -ePATTERN | -f FILE ][ FILE … ]

  8. grep(1) Man Page (cont.) • OPTIONS • -c only prints a count of matching lines • -i ignores letter case distinctions • -l only prints list of names of files with matches • -n prefixes line numbers to matching lines • -q is quiet, returning only appropriate exit status • -v selects variant or non-matching lines • -ePATTERN makes pattern explicit,even if starting with “-” • -f FILE takes list of patterns from file, one per line

  9. Questions?

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