I have a text file named test.txt in current directory.now I want to output test.txt's first line and its last line to the terminal with cat text.txt | (head -1 ; tail -1), but the result is that it only outputs the first line to the terminal.
How do I output the first line and the last line using a single command?
The problem with your command is that only the 1st command - head -1 - receives the stdin input, because it consumes it on reading, so that the 2nd command - tail -1 - receives no input.
In this particular case, you can use command grouping ({ ...; ...; }):
{ head -1; tail -1; } < text.txt Caveats:
The above only works with seekable input, meaning either a regular file, a here-string or here-doc.
cat text.txt | { head -1; tail -1; }) or with input from a process substitutions ({ head -1; tail -1; } < <(cat text.txt)), because such input is not seekable (tail cannot scan from the end backward).Even with seekable input this is not a generic method to send input to multiple commands at once.
tail reads backwards from the end of the (seekable) input, irrespective of whether all the input has already been read or not.As a simpler alternative that works generically, here's a sed solution:
sed -n '1p; $p' text.txt -n suppresses output of lines by default1p matches line 1 and prints it (p).$p matches the last line ($) and prints it.You could use awk.
awk 'NR==1{print}END{print}' file Using tee:
cat text.txt | tee >(head -1) >(tail -1) > /dev/null 
