Bash – awk – combine two filters into one

awkbashscripting

I have this variable in a bash script on ubuntu 12.04 which is set to show the available MB on the root partition:

AV_MB=$(df -m |awk NR==2 |awk '{print $4}')

Is there an elegant way to combine these two awk expressions into one? Or a shorter way with sed or grep or cut?

Best Answer

Awk works on the "pattern {action}" model, so you can combine those two processes into a single and correct:

 df -m | awk 'NR==2 {print $4}'

This, however, is fragile as the second record could change (on my systems, the root record is the third row), so you can match on the final field of the record for the root filesystem, like so:

df -m | awk '$NF == "/" {print $4}'

which ensures your pattern matches wherever df prints /.

Related Solutions

Improving the AWK skills

awk -v copies=3 -v spacer=_ '
  BEGIN {OFS=FS=","} 
  {
    field1 = $1
    for (i=1; i <= copies+1; i++) {
      $1 = sprintf("%s%s%03d", field1, spacer, i)
      print
    }  
    print ""
  }
'

This takes advantage of awk recalculating $0 if any of the fields change value.

Bash – awk + set variable inside the awk

Do you want something like this?

function get_column
{ 
    awk -v val=$1 '{print $val}' list.txt
}

Above is returning the column match with $1 passing to the function. if you really need print the line match with line number in $1 from function, instead use below.

function get_row
{ 
    awk -v val=$1 'NR==val{print ; exit}' list.txt
}

Or let shell evaluated and set the val value and print that within awk as following:

function get_column
{ 
    awk '{print $val}' val=$1 list.txt
}

function get_row
{ 
    awk 'NR==val{print ; exit}' val=$1 list.txt
}

Here you are passing val with only numbers and if val was contain backslash escape character you will encounter a problem which awk does C escape sequence processing on values passed via -v val= and a shell variable with val="\\n" will change to value with \n by awk.

Best Answer

Related Solutions

Improving the AWK skills

Bash – awk + set variable inside the awk

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