Delete First line of a file
An alternative very lightweight option is just to 'tail' everything but the first line (this can be an easy way to remove file headers generally):
# -n +2 : start at line 2 of the file.
tail -n +2 file.txt > file.stdout
Following @Evan Teitelman, you can:
tail -n +2 file.txt | sponge file.txt
To avoid a temporary file. Another option might be:
echo "$(tail -n +2 file.txt)" > file.txt
And so forth. Testing last one:
[user@work ~]$ cat file.txt
line 1
line 2
line 3
line 4
line 5
[user@work ~]$ echo "$(tail -n +2 file.txt)" > file.txt
[user@work ~]$ cat file.txt
line 2
line 3
line 4
line 5
[user@work ~]$
Oops we lost a newline (per @1_CR comment below), try instead:
printf "%s\n\n" "$(tail -n +2 file.txt)" > file.txt
[user@work ~]$ cat file.txt
line 1
line 2
line 3
line 4
line 5
[user@work ~]$ printf '%s\n\n' "$(tail -n +2 file.txt)" > file.txt
[user@work ~]$ cat file.txt
line 2
line 3
line 4
line 5
[user@work ~]$
Coming back to sed, try:
printf '%s\n\n' "$(sed '1d' file.txt)" > file.txt
or perhaps
echo -e "$(sed '1d' file.txt)\n" > file.txt
To avoid side effects.
The reason file.txt is empty after that command is the order in which the shell does things. The first thing that happens with that line is the redirection. The file "file.txt" is opened and truncated to 0 bytes. After that the sed command runs, but at the point the file is already empty.
There are a few options, most involve writing to a temporary file.
sed '1d' file.txt > tmpfile; mv tmpfile file.txt # POSIX
sed -i '1d' file.txt # GNU sed only, creates a temporary file
perl -ip -e '$_ = undef if $. == 1' file.txt # also creates a temporary file
This topic is interest, so I test the benchmark in 3 ways:
sed '1d' d.txt > tmp.txttail -n +2 d.txt > tmp.txtsed -i '1d' d.txt
Note that target d.txt is 5.4GB file
Get the result :
run 1 : sed '1d' d.txt > r1.txt
14s
run 2 : tail -n +2 d.txt > r2.txt
20s
run 3 : sed -i '1d' d.txt
88s
Conclusion : It seems below be the quickest way:
sed '1d' file.txt > tmpfile; mv tmpfile file.txt