Searching Files with grep
grep prints lines from files which match a pattern
For example, to find an entry in the password file
/etc/passwd relating to the user ‘nancy’:
$ grep nancy /etc/passwd
grep has a few useful
options:
- -
- -r searches through files
in specified directories, recursively
- -l prints just the names
of files which contain matching lines( stands for "show the file name, not the result itself`.)
- -c prints the count of
matches in each file
- -n numbers the matching
lines in the output
- -v reverses the test, printing lines which don’t match
- R stands for recursive.
Patter Matching
Use grep to fid patters, as we as simple
Patters are expressed
as reguar expressios
grep -Ril "text-to-find-here" /
grep -Ril "text-to-find-here" /
Certain punctuation characters have special
For example this might
be a better way to search for acy’s etry i the password fie:
$ grep ’ˆacy’ /etc/passwd
The caret (ˆ) achors the patter to the start of the ie
I the same way, $ acts as a achor whe it appears at the ed of a strig,
makig the
patter match oy at
the ed of a ie
44
iux System Administration Module 7.
Search Text Fies Using Regular
Matching Repeated
Patters
Some regexp specia
characters are aso specia to the she, ad so eed to be protected with
Quotes or backsashes
We ca match a repeatig
patter by addig a modifier:
$ grep -i ’cotiued\.*’
Dot (.) o its own would match ay character, so to match an
actua dot we escape it with \
The * modifier matches the precedig character zero or more
times
Simiary, the \+ modifier matches oe or more times
Matchig Aterative
Patters
Mutipe subpatters ca
be provided as ateratives, separated with \|, for example:
$ grep ’fish\|chips\|pies’
food.txt
The previous commad
fids ies which match at east oe of the words
Use \(...\) to eforce precedence:
$ grep -i ’\(cream\|fish\|birthday\)
cakes’ deicacies.txt
Use square brackets
to buid a character cass:
$ grep’ [Jj]oe [Bb]oggs’
staff.txt
Any singe character
from the class matches; ad rages of characters ca be expressed as
‘a-z’
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