Unix: awk save values as variable

Question

I have a filename with several underscores:

nc_glals_3_4.mrc

and there I can read out the values 3 and 4 with awk:

$ echo "nc_glals_3_4.mrc" | awk -F'[_.]' '{print$3$4}' 
34

But if I like to store 34 as a variable and recall the variable, it does not work:

$ variable=$("nc_glals_3_4.mrc" | awk -F'[_.]' '{print $3$4}')
-bash: nc_glals_3_4.mrc: command not found

$ variable="$("nc_glals_3_4.mrc" | awk -F'[_.]' '{print $3$4}')"
-bash: nc_glals_3_4.mrc: command not found

$ variable
-bash: variable: command not found

What's wrong?

variable=$(echo "nc_glals_3_4.mrc" | awk -F'[_.]' '{print $3$4}') — jhnc
– jhnc, Commented Dec 2, 2020 at 22:50
You need echo inside of $( . . . ) just like on the outside. Bash is attempting to run your string as a program — dawg
– dawg, Commented Dec 3, 2020 at 1:08

louigi600 · Accepted Answer · 2020-12-03 06:48:21Z

2

If the numbers you want to retain are always in the same position:

test@darkstar:~$ Filename="nc_glals_3_4.mrc"
test@darkstar:~$ awk -F'[_.]' '{print$3$4}' <<< $Filename
34
test@darkstar:~$ Numbers=$(awk -F'[_.]' '{print$3$4}' <<< $Filename)
test@darkstar:~$ echo $Numbers
34
test@darkstar:~$

But if the numbers are not always in the same position and you want to catch all numbers between underscores or between underscore and full stop no matter where they occour:

Numbers=$(awk -F'[_.]' '{for (i=0;i<=NF;i++) {if ($i~/^[0-9]+$/) {printf("%i", $i)}}}' <<< $Filename)

answered Dec 3, 2020 at 6:48

louigi600

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Comments

giovannipa · Accepted Answer · 2020-12-02 22:50:54Z

1

If I understand your question:

variable=$(echo "nc_glals_3_4.mrc" | awk -F'[_.]' '{print $3$4}')

You need an echo in your command.... now '34' is stored into variable.

answered Dec 2, 2020 at 22:50

giovannipa

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Comments

markp-fuso · Accepted Answer · 2020-12-02 23:24:13Z

1

Just as you used echo on the command line, you also need to use echo in the sub-process call, eg:

# wrong:

$ variable=$("nc_glals_3_4.mrc" | awk -F'[_.]' '{print $3$4}')

# right:

$ variable=$(echo "nc_glals_3_4.mrc" | awk -F'[_.]' '{print $3$4}')

# or using here string:

$ variable=$(awk -F'[_.]' '{print $3$4}' <<< "nc_glals_3_4.mrc")

Then use echo again to display the variable's value:

$ echo "${variable}"
34

edited Dec 2, 2020 at 23:24

answered Dec 2, 2020 at 23:17

markp-fuso

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