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Can anyone please explain to me in brief about the syntax of this command? I know the output of this command but want to learn how it is working.

I expect an explanation in terms of how actually this command is written and significance of each and every character used in the command.

sed -i 's|\(LAYOUT PATH \).*|\1 "../GDS/'$1'.gds"|g' drcCustimize2 
  • First you have looked at the man page for sed and realize that this will edit the file (i.e. change and replace it with the edited contents). – mdpc Aug 26 '14 at 6:06
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  • sed: Call the sed command
  • -i: Pass sed the -i option: Modify the file in-place
  • 's|\(LAYOUT PATH \).*|\1 "../GDS/'$1'.gds"|g': The '...'$1'..' are used to make this whole part one single argument to the sed command
  • s|\(LAYOUT PATH \).*|\1 "../GDS/'$1'.gds"|g:
    • s|pattern|replacement|options: s is the substitute (or search and replace) command, the | characters are used to separate the parts of that command from each other
    • \(LAYOUT PATH \): Search for the literal string "LAYOUT PATH ", and capture it into a group; the content of this group can be put into the replacement string using \1
    • .*: Match everything until the end of the line
    • \1: Put the matched group 1 into the replacement text
    • "../GDS/: Put the literal string "../GDS/ into the replacement text
    • $1: Put the first argument to the shell-script into the replacement text
    • .gds": Put the literal string .gds" into the replacement
    • g: Do the replacement for every match on a line; without the g, only the first match is replaced
    • drcCustimize2: The file that sed should change
  • Thanks a lot Daniel for clear explanation Regards Madhvi – yisha Aug 26 '14 at 7:14
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    Strictly speaking 's|\(LAYOUT PATH \).*|\1 "../GDS/'$1'.gds"|g' doesn't necessarily make up one argument because $1 is not quoted so the split+glob operator applies here. 's|\(LAYOUT PATH \).*|\1 "../GDS/'"$1"'.gds"|g' would be correct. – Stéphane Chazelas Aug 26 '14 at 9:27
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    Also, the g is useless, as a pattern ending with .* cannot possibly match a line more than once. – G-Man Says 'Reinstate Monica' Aug 26 '14 at 21:35

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