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grep -i "^(.).*\1$" sowpods.txt > output.txt

I'm using a scrabble words list I downloaded named "sowpods.txt" and I am trying to use grep to find all of the 7 letter words in the file that start and end with the same letter .The line I have now is giving me a backreference error so I tried using online guides but they were insanely confusing. Could someone help me do this? Thanks!

I'm also on a mac and am using the default terminal.

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This will work as an extended regular expression. You need grep -E:

grep -E -i "^(.).*\1$"

To match 7-letter words you need to replace * with {5}:

grep -E -i "^(.).{5}\1$"
  • I'm a fan of the -x flag: grep -Eix "(.).{5}\1" – Jim L. Jan 30 at 22:46
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If you want to use basic regular expression (without option -E), you need a backslash \ before the opening and closing brackets:

grep -i '^\(.\).\{5\}\1$' file

Note that it's good idea to use single quote in your grep regex in order to avoid shell parameter expansion.

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