Linux Command Library
commands
Commands
basic
Basic
tips
Tips

look

display lines beginning with a given string

- Look for lines which begins with the given prefix:
look prefix file

- Look for lines ignoring case:
look -f prefix file

[-bdf ] [-t termchar ] string [file ... ]

The utility displays any lines in file which contain string as a prefix.

If file is not specified, the file /usr/share/dict/words is used, only alphanumeric characters are compared and the case of alphabetic characters is ignored.

The following options are available:

-b
Use a binary search on the given word list. If you are ignoring case with -f or ignoring non-alphanumeric characters with -d the file must be sorted in the same way. Please note that these options are the default if no filename is given. See sort(1) for more information on sorting files.
-d
Dictionary character set and order, i.e., only alphanumeric characters are compared.
-f
Ignore the case of alphabetic characters.
-t
Specify a string termination character, i.e., only the characters in string up to and including the first occurrence of termchar are compared.

The LANG , LC_ALL and LC_CTYPE environment variables affect the execution of the utility. Their effect is described in environ(7).

/usr/share/dict/words
the dictionary

The utility exits 0 if one or more lines were found and displayed, 1 if no lines were found, and >1 if an error occurred.

The original manual page stated that tabs and blank characters participated in comparisons when the -d option was specified. This was incorrect and the current man page matches the historic implementation.

uses a linear search by default instead of a binary search, which is what most other implementations use by default.

grep(1), sort(1)

A utility appeared in AT&T System v7 .

Lines are not compared according to the current locale's collating order. Input files must be sorted with LC_COLLATE set to `C'

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