Unix Tips And Tricks

Unix_Tips_n_Tricks.md

Awk

Print only the first part of a file separated by two newlines

Note that this uses tr to remove any carriage-returns (as in "\r\n" from Windows or network programs)

# Print only the block of lines before the first double-newline
cat file.txt | tr -d '\r' | \
  awk 'BEGIN {RS="\n\n"} NR==1'
  
# Print every block of lines after the first double newline
cat file.txt | tr -d '\r' | \
  awk 'BEGIN {RS="\n\n"} NR>=2'

And here's a very ugly version of the same using multi-dimensional arrays. Set 'z=' to the index you want to print. In this example, it'll print the second block of lines after the first double-newline. (note that this is removing the empty line using getline)

cat file.txt | tr -d '\r' | \
  awk 'BEGIN {i=0; n=0; z=1}; 
       $0 ~ /^$/ { n++; getline; }; { a[n][i]=$0; i++ };
       END { for(i in a[z]) print a[z][i] }'

Useful Links

• https://catonmat.net/awk-one-liners-explained-part-one
• https://catonmat.net/ten-awk-tips-tricks-and-pitfalls
• https://catonmat.net/ftp/awk.cheat.sheet.txt
• https://www.gnu.org/software/gawk/manual/html_node/index.html#SEC_Contents