Concatenate FILE(s), or standard input, to standard output.
cat [Options] [File]...
-A, --show-all equivalent to -vET -b, --number-nonblank number nonblank output lines -e equivalent to -vE -E, --show-ends display $ at end of each line -n, --number number all output lines -s, --squeeze-blank never more than one single blank line -t equivalent to -vT -T, --show-tabs display TAB characters as ^I -u (ignored) -v, --show-nonprinting use ^ and M- notation, except for LFD and TAB --help display this help and exit --version output version information and exit
With no FILE, or when FILE is -, read standard input.
The cat command can be piped into grep to find specific words in the file:
cat file.txt | grep keyword output.txt
However all modern versions of grep have this built-in. Running a single command/process is more efficient, and so with large files will be noticably faster:
grep keyword file.txt output.txt
grep can also display an entire file, (like cat), by using the grep keyword “.” which will match lines with at least 1 character. Alternatively the grep keyword “^” will match the beginning of every line including blank lines.
When grep is used to display multiple files, it will prepend each line of output with the filename:
$ grep . *.txt
Display a file:
$ cat myfile.txt
Display all .txt files:
$ cat *.txt
Concatenate two files:
$ cat File1.txt File2.txt > union.txt
If you need to combine two files but also eliminate duplicates, this can be done with sort unique:
$ sort -u File1.txt File2.txt > unique_union.txt
Put the contents of a file into a variable
$ my_variable=`cat File3.txt`