merge file text with file name

Question

I have two text files. The first "file1.txt" has content:

Apple
Orange
Banana

while the second file "file2.txt" has content:

monday
tuesday
wednesday

I want to combine them into one file and its output is:

Apple       File1.txt
Orange      File1.txt
Banana      File1.txt
monday      File2.txt
tuesday     File2.txt
wednesday   File2.txt

Answer 1

That's quite trivial with awk:

$ awk '{print $0,FILENAME}' File*.txt
Apple File1.txt
Orange File1.txt
Banana File1.txt
monday File2.txt
tuesday File2.txt
wednesday File2.txt

If you want a tab rather than a space between the input line and the filename, add -v OFS='\t' to the command-line to set the Output Field Separator (OFS):

awk -v OFS='\t' '{print $0,FILENAME}' File*.txt

or use:

awk '{print $0 "\t" FILENAME}' File*.txt

That's assuming file names don't contain = characters. If you can't guarantee that the filenames won't contain = characters, you can change that to:

awk '{print $0 "\t" substr(FILENAME, 3)}' ./File*.txt

Though with GNU awk at least, you'd then get warnings if the name of the file contained bytes not forming valid characters (which you could work around by fixing the locale to C (with LC_ALL=C awk...) though that would also have the side effect of potentially changing the language of other error messages if any).

Answer 2

With perl:

perl -lpe '$_ .= "\t$ARGV"' File*.txt

(note that it's fine with a glob like File*.txt but could be dangerous with different ones).

Answer 3

For interactive use on the command line, one of the easiest things to type is

grep . File*.txt

Since the regex . matches any character, every non-empty line of every file will match, and be printed with the filename as a prefix.

It's great for use-cases like checking some kernel settings that are stored with one setting per file:

$ grep . /sys/kernel/mm/transparent_hugepage/*
/sys/kernel/mm/transparent_hugepage/defrag:[always] defer defer+madvise madvise never
/sys/kernel/mm/transparent_hugepage/enabled:[always] madvise never
/sys/kernel/mm/transparent_hugepage/hpage_pmd_size:2097152
grep: /sys/kernel/mm/transparent_hugepage/khugepaged: Is a directory
/sys/kernel/mm/transparent_hugepage/shmem_enabled:always [within_size] advise never deny force
/sys/kernel/mm/transparent_hugepage/use_zero_page:1