bash - Linux: why doesnt sed -e '1,244d' remove -


why doesn't sed -e '1,244d' remove first 244 lines of text file. i've used code many time albeit smaller line counts here copy of code:

    sed -e '1,244d' /home/user/documents/working_files/storage/file.txt <> /home/user/documents/working_files/storage/file.txt

i test script in bash , nothing happens, run under sudo , displays script modified per script, not append/overwrite file, used "<>" option try script clear un-needed , not have append new file. appeciated. help

short answer

you can use

command < file | sponge file

so in case:

sed -e '1,244d' file | sponge file

sponge (moreutils) command soaks stdin memory , when finished writes file. enables 1 "inline" modifications.

fair warning inline modifications

first of warning: don't inline replacements. if server crashes in middle of process, file can corrupted, , case can have lost both original , new file. sponge cannot undo effect: use sed -e '1,244d' file | sponge file possible sed finishes job, , sponge starts writing file. in middle of process machine crashes , content of original file gone , can recover part sponge wrote.

you better use:

command < file > tempfile mv -f tempfile file

as @charlesduffy suggests.

which more atomic version of:

command < file > tempfile cp tempfile file rm tempfile

so in case machine crashes (for instance there power failure) @ part, have @ least or original file; or resulting file.

the problem diamond operator <>

the diamond operator has specification hard understand:

[j]<>filename       #  open file "filename" reading , writing,       #+ , assign file descriptor "j" it.       #  if "filename" not exist, create it.       #  if file descriptor "j" not specified, default fd 0, stdin.

it means both reading , writing assigned stdin, not reading stdin , writing stdout. diamond operator cannot used automatic inline replacement, unless program uses file descriptors bidirectionally.

bidirectional processing

as said, there exist utility programs sponge allow store result temporary in memory , saves file when stdin closes.

sed specific inline edits

sed has --in-place flag:

-i[suffix], --in-place[=suffix]         edit files in place (makes backup if suffix supplied)

so running:

sed -e '1,244d' -i file

you can inline modifications.


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