How to make GREP select only numeric values

Question

I use the df command in a bash script   df   -B MB   tail -1   awk   print  4     grep    0-9     This script returns   99    But I need only numbers  to make the next comparison   If I use the grep regex without the dot   df   -B MB   tail -1   awk   print  4     grep    0-9     I receive nothing  How to fix

User · Accepted Answer

If you try    echo  99    grep -o   0-9      It returns   99     Here s the details on the -o  or --only-matching flag  works from the grep manual page      Print only the matched  non-empty  parts of matching lines  with each such part on a separate output line  Output lines use the same delimiters as input  and delimiters are null bytes if -z  --null-data  is also used  see Other Options

User · Answer

function getPercentUsed          sys   system  df -h  dev sda6 --output pcent   grep -o   0-9       val       return  val 0

User · Answer

No need to used grep here  Try this   df   -B MB   tail -1   awk   print substr  5  1  length  5 -1

User · Answer

Don t use more commands than necessary  leave away tail  grep and cut  You can do this with only  a simple  awk  PS  giving a block-size en print only de persentage is a bit silly  -  So leave also away the  -B MB      df    awk -F  multiple field seperators     NF   Last field must be exactly --  mounted patition   print   NF-number from last field      in your case  use   df    awk -F         NF       print   NF-2      output  81  If you want to show the percent symbol  you can leave the -F       away and your print field will move 1 field further back  df    awk   NF       print   NF-1      output  81

User · Answer

grep will print any lines matching the pattern you provide  If you only want to print the part of the line that matches the pattern  you can pass the -o option      -o  --only-matching   Print only the matched  non-empty  parts of a matching line  with each such part on a separate output line    Like this   echo  Here is a line mentioning 99  somewhere    grep -o   0-9

User · Answer

How about   df   -B MB   tail -1   awk   print  4     cut -d    -f1

User · Answer

You can use Perl style regular expressions as well  A digit is just  d then  grep -Po  quot   d  quot  filename  -P Interpret PATTERNS as Perl-compatible regular expressions  PCREs   -o Print only the matched  non-empty  parts of a matching line  with each such part on a separate output line

[linux] How to make GREP select only numeric values?

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