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J. Doe
Asked: 2018-06-01 11:36:14 +0800 CST

Ignoring an output with grep

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I am currently using grep to locate a string in a file. However, I get a result I do not want.

Example output:

user@user:~/tmp$ grep "z=" note > tmp.txt | cat tmp.txt 
z=0.016728
 S_1.4 GHz=   1597.61548     mJy, for L_1.4=1E24 W Hz^-1 (index=0.8)

I do not want to use grep to ignore all results after z=0.016728 because I cannot guarantee that the file structure I am using will always have z= before GHz=.

I would like to ignore anything without a newline or with a character value before z=.

grep

2 Answers

  1. Best Answer

    Based on the sample you have given, the simplest option would be to anchor the expression to the start of a line:

    grep '^z=' note

    Alternatively, you could match only after a word boundary:

    grep '\bz=` note

    See Start of String and End of String Anchors and Word Boundaries

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  2. Reread man grep, and use Extended grep with a simple Regular expression (and single quotes to avoid shell expandion always): 

    grep -E '^z=' note
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