Rename file as third word on it (bash)-CodePudding

I have several autogenerated files (see the picture below for example) and I want to rename them according to 3rd word in the first line (in this case, that would be 42.txt).

First line:

ligand CC@@HOc3ccccc3 42 P10000001

Is there a way to do it?

CodePudding user response：

Say you have file.txt containing:

ligand CC@@HOc3ccccc3 42 P10000001

and you want to rename file.txt to 42.txt based on the 3rd field in the file.

*Using awk

The easiest way is simply to use mv with awk in a command substitution, e.g.:

mv file.txt $(awk 'NR==1 {print $3; exit}' file.txt).txt

Where the command-substitution $(...) is just the awk expression awk 'NR==1 {print $3; exit}' that simply outputs the 3rd-field (e.g. 42). Specifying NR==1 ensures only the first line is considered and exit at the end of that rule ensures no more lines are processed wasting time if file.txt is a 100000 line file.

Confirmation

file.txt is now renamed 42.txt, e.g.

$ cat 42.txt
ligand CC@@HOc3ccccc3 42 P10000001

Using read

You can also use read to simply read the first line and take the 3rd word as the name there and then mv the file, e.g.

$ read -r a a name a <file.txt; mv file.txt "$name".txt

The temporary variable a above is just used to read and discard the other words in the first line of the file.