[SOLVED] Replacing the value of specific field in a table-like string stored as bash variable

Issue

I am looking for a way to replace (with 0) a specific value (1043252782) in a "table-like" string stored as a bash variable. The output of echo "$var"looks like this:

  5 Reallocated_Sector_Ct   0x0033   100   100   010    Pre-fail  Always       -       0
  7 Seek_Error_Rate         0x000f   090   060   045    Pre-fail  Always       -       1043252782
 10 Spin_Retry_Count        0x0013   100   100   097    Pre-fail  Always       -       0
187 Reported_Uncorrect      0x0032   100   100   000    Old_age   Always       -       0

After the replacement echo "$var" should look like this:

  5 Reallocated_Sector_Ct   0x0033   100   100   010    Pre-fail  Always       -       0
  7 Seek_Error_Rate         0x000f   090   060   045    Pre-fail  Always       -       0
 10 Spin_Retry_Count        0x0013   100   100   097    Pre-fail  Always       -       0    
187 Reported_Uncorrect      0x0032   100   100   000    Old_age   Always       -       0

Is there a way to do this without saving the content of $var to a file and directly manipulating it within the bash (shell script)?

Maby with awk? I can select the value in the 10th field of the second record with awk and pattern matching ("7 Seek_Error_Rate ....") like this:

echo "$var" | awk '/^  7/{print $10}'

Maby there is some way doing it with awk (or other cli-tool) to replace it and store it back into $var? Also, the value changes over time, but the structure remains the same (some record at the 10th field).

Solution

You can change a specific string directly in the shell:

var=${var/1043252782/0}

To replace final number of second line, you could use awk or sed:

var=$(awk 'NR==2 { sub(/[0-9]+$/,0) }1' <<<"$var")

var=$(sed '2s/[0-9][0-9]*$/0/' <<<"$var")

If you don't know which line it will be, you can match a known string:

var=$(awk '/Seek_Error_Rate/{ sub(/[0-9]+$/,0) }1' <<<"$var")

var=$(sed '/Seek_Error_Rate/s/[0-9][0-9]*$/0/' <<<"$var")

Answered By - jhnc

Answer Checked By - Timothy Miller (WPSolving Admin)