Useful bash Pieces

• Remove all non-digit characters from a string (source):

  echo toto.titi.12.tata.2.abc.def | tr -d -c 0-9

• Insert a line into a file. Example inserts between lines 2 & 3, and assumes file is <=1000 lines long.

  oldfile=file.json

  sed -n 1,2p $oldfile>tempfile.json

  echo "put this text in new line" >>tempfile.json

  sed -n 3,1000p $oldfile>>tempfile.json

  mv tempfile.json $oldfile

For JSON manipulation:

• Remove characters from end of string. Example is final 4.

  echo ${variable%????}

• Pull the line containing “RepetitionTime” from a JSON file; keep characters after colon; strip the trailing comma:

  tr=`more $jsonfile | grep "RepetitionTime"`

  tr=`echo ${tr#*:} | sed 's/.$//'`