4.4. grep with Pipes

Instead of taking its input from a file, grep often gets its input from a pipe.

Example 4.29.

% ls -l

drwxrwxrwx  2  ellie    2441 Jan 6 12:34    dir1

-rw-r--r--  1  ellie    1538 Jan 2 15:50    file1

-rw-r--r--  1  ellie    1539 Jan 3 13:36    file2

drwxrwxrwx  2  ellie    2341 Jan 6 12:34    grades



% ls -l | grep '^d'

drwxrwxrwx  2  ellie    2441 Jan 6 12:34    dir1

drwxrwxrwx  2  ellie    2341 Jan 6 12:34    grades

EXPLANATION

The output of the ls command is piped to grep. All lines of output that begin with a d are printed; that is, all directories are printed.

4.4.1 grep Review

Table 4.3 contains examples of grep commands and what they do.

Table 4.3. Review of grep

Command	What It Does
grep '\<Tom\>' file	Prints lines containing the word Tom.
grep 'Tom Savage' file	Prints lines containing Tom Savage.
grep '^Tommy' file	Prints lines if Tommy is at the beginning of the line.
grep '\.bak$' file	Prints lines ending in .bak. Single quotes protect the dollar sign ($) from interpretation.
grep '[Pp]yramid' *	Prints lines from all files containing pyramid or Pyramid in the current working directory.
grep '[A–Z]' file	Prints lines containing at least one capital letter.
grep '[0–9]' file	Prints lines containing at least one number.
grep '[A–Z]...[0–9]' file	Prints lines containing five-character patterns starting with a capital letter and ending with a number.
grep –w '[tT]est' files	Prints lines with the word Test and/or test.
grep –s 'Mark Todd' file	Finds lines containing Mark Todd, but does not print the lines. Can be used when checking grep's exit status.
grep –v 'Mary' file	Prints all lines not containing Mary.
grep –i 'sam' file	Prints all lines containing sam, regardless of case (e.g., SAM, sam, SaM, sAm).
grep –l 'Dear Boss' *	Lists all filenames containing Dear Boss.
grep –n 'Tom' file	Precedes matching lines with line numbers.
grep "$name" file	Expands the value of variable name and prints lines containing that value. Must use double quotes.
grep '$5' file	Prints lines containing literal $5. Must use single quotes.
ps –ef| grep '^ *user1'	Pipes output of ps –ef to grep, searching for user1 at the beginning of a line, even if it is preceded by zero or more spaces.