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Full Discussion: Basic grep question
Top Forums Shell Programming and Scripting Basic grep question Post 303002507 by kraljic on Saturday 26th of August 2017 01:50:11 AM
Old 08-26-2017
Basic grep question

Shell : Bash shell (Fedora 26)

In the below text file (output.txt), I need to find all lines starting with the pattern pc. As you can see, only one line matches this condition (pc hello world).

But, my below 3 attempts return wrong output. How do I use the grep command correctly here ?


Code:
 # cat output.txt
  sunrpc                331776  1
  crct10dif_pclmul       16384  0
  crc32_pclmul           16384  0
  shpchp                 36864  0
  snd_pcm               102400  4 snd_hda_intel,snd_hda_codec,snd_hda_core,snd_hda_codec_hdmi
  snd_timer              32768  2 snd_seq,snd_pcm
  lpc_ich                24576  0
  pc hello world

  # Attempt1
  # It returns any line with the the pattern pc in it which is not what I want
  # grep 'pc' output.txt
  sunrpc                331776  1
  crct10dif_pclmul       16384  0
  crc32_pclmul           16384  0
  shpchp                 36864  0
  snd_pcm               102400  4 snd_hda_intel,snd_hda_codec,snd_hda_core,snd_hda_codec_hdmi
  snd_timer              32768  2 snd_seq,snd_pcm
  lpc_ich                24576  0
  pc hello world
  # 


  # Attempt2
  # No output returned at all
  # grep 'pc^' output.txt



  # Attempt3 
  # I think this gives the same wrong output as Attempt1 
  # grep 'pc*' output.txt
  sunrpc                331776  1
  crct10dif_pclmul       16384  0
  crc32_pclmul           16384  0
  shpchp                 36864  0
  snd_pcm               102400  4 snd_hda_intel,snd_hda_codec,snd_hda_core,snd_hda_codec_hdmi
  snd_timer              32768  2 snd_seq,snd_pcm
  lpc_ich                24576  0
  pc hello world
  #

 

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GREP(1) 						      General Commands Manual							   GREP(1)

NAME
grep - search a file for a pattern SYNOPSIS
grep [ option ... ] pattern [ file ... ] DESCRIPTION
Grep searches the input files (standard input default) for lines (with newlines excluded) that match the pattern, a regular expression as defined in regexp(6). Normally, each line matching the pattern is `selected', and each selected line is copied to the standard output. The options are -c Print only a count of matching lines. -h Do not print file name tags (headers) with output lines. -i Ignore alphabetic case distinctions. The implementation folds into lower case all letters in the pattern and input before interpre- tation. Matched lines are printed in their original form. -l (ell) Print the names of files with selected lines; don't print the lines. -L Print the names of files with no selected lines; the converse of -l. -n Mark each printed line with its line number counted in its file. -s Produce no output, but return status. -v Reverse: print lines that do not match the pattern. Output lines are tagged by file name when there is more than one input file. (To force this tagging, include /dev/null as a file name argument.) Care should be taken when using the shell metacharacters $*[^|()= and newline in pattern; it is safest to enclose the entire expression in single quotes '...'. SOURCE
/sys/src/cmd/grep.c SEE ALSO
ed(1), awk(1), sed(1), sam(1), regexp(6) DIAGNOSTICS
Exit status is null if any lines are selected, or non-null when no lines are selected or an error occurs. GREP(1)
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