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I have a file with a lot of lines like this

0       file:/home/knappen/somefilename.txt  7       0.2838356973995272      19      0.21823286052009455     18      0.10121158392434988     15      0.07816193853427897     11
  0.07284278959810875     6       0.056885342789598115    8       0.03738179669030733     22      0.032062647754137114    23      0.01610520094562648     12      0.01610520094562648     16      0.010786052009456266    0       0.010786052009456266    13      0.009013002364066195    5       0.009013002364066195    10      0.007239952718676124    9       0.007239952718676124    14      0.005466903073286052    4       0.005466903073286052    21      0.003693853427895981    20      0.003693853427895981    17      0.003693853427895981    3       0.003693853427895981    2       0.003693853427895981    1
   0.003693853427895981

and I want to select all rows where the entry in the third columns equals to some given number.

I know how to write a pattern for grep -E for this purpose or to write a small python or perl script with this effect, but I wonder whether there is an elegant solution using GNU coreutils.

P.S. I found some answers with good suggestions in this question Selecting rows in a CSV file based on column value, but the tools are beyond GNU coreutils. The answers there are good enough to work for me, but for the sake of learning more about the power of the shell utilities I ask this question anyhow.

3

Awk is a pretty powerful tool for text-formatting/manipulation and pattern matching. It de-limits each line of the file with a custom de-limiter with default being a single white-space. Once split the individual fields can be accessed from $1,$2..$N, where N is the last column number in the line.

So to your requirement just match the third column with the value you need

awk '$3 == "string"' file 

If the file is a CSV which has a different de-limiter, e.g. , just define it as

awk -v FS="," '$3 == "string"' file

Also awk is not GNU specific, its variant should be available across *nix machines and also POSIX compliant.

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