How does sponge (from moreutils) work?
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sponge can “soak up” stdin and write it atomically to a file, enabling one to do cat f|sponge a. I want to know how exactly it accomplishes this. How does it know when the input is finished?
shell io-redirection stdout stdin
edited yesterday
Jeff Schaller
36.3k952120
asked yesterday
HappyFace
27111
add a comment |
up vote
1
down vote
favorite
sponge can “soak up” stdin and write it atomically to a file, enabling one to do cat f|sponge a. I want to know how exactly it accomplishes this. How does it know when the input is finished?
shell io-redirection stdout stdin
edited yesterday
Jeff Schaller
36.3k952120
asked yesterday
HappyFace
27111
2
What do you mean? The same way every other program knows (e.g.cat f | wcorcat f | grep fooor whatever), why would you expectspongeto be special?
– terdon♦
yesterday
add a comment |
up vote
1
down vote
favorite
up vote
1
down vote
favorite
sponge can “soak up” stdin and write it atomically to a file, enabling one to do cat f|sponge a. I want to know how exactly it accomplishes this. How does it know when the input is finished?
shell io-redirection stdout stdin
edited yesterday
Jeff Schaller
36.3k952120
asked yesterday
HappyFace
27111
sponge can “soak up” stdin and write it atomically to a file, enabling one to do cat f|sponge a. I want to know how exactly it accomplishes this. How does it know when the input is finished?
shell io-redirection stdout stdin
shell io-redirection stdout stdin
edited yesterday
Jeff Schaller
36.3k952120
asked yesterday
HappyFace
27111
edited yesterday
Jeff Schaller
36.3k952120
asked yesterday
HappyFace
27111
edited yesterday
Jeff Schaller
36.3k952120
edited yesterday
Jeff Schaller
36.3k952120
edited yesterday
Jeff Schaller
36.3k952120
36.3k952120
asked yesterday
HappyFace
27111
asked yesterday
HappyFace
27111
asked yesterday
HappyFace
27111
27111
2
What do you mean? The same way every other program knows (e.g.cat f | wcorcat f | grep fooor whatever), why would you expectspongeto be special?
– terdon♦
yesterday
add a comment |
2
What do you mean? The same way every other program knows (e.g.cat f | wcorcat f | grep fooor whatever), why would you expectspongeto be special?
– terdon♦
yesterday
2
2
What do you mean? The same way every other program knows (e.g.
cat f | wc or cat f | grep foo or whatever), why would you expect sponge to be special?– terdon♦
yesterday
What do you mean? The same way every other program knows (e.g.
cat f | wc or cat f | grep foo or whatever), why would you expect sponge to be special?– terdon♦
yesterday
add a comment |
1 Answer
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oldest
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3
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accepted
strace or similar will show the system calls used by sponge, which is probably to write(2) the input read(2) from standard input out to a temporary file, and then to rename(2) that temporary file to the desired output filename when the input ends. The input ends when a read(2) call fails or returns 0 (which indicates end-of-file) at which point sponge can do the rename.
answered yesterday
thrig
23.6k12955
And when therename()fails with EXDEV when/tmpis on a different file system, it ends up copying the data again into the destination file. You can avoid that by settingTMPDIRto$(dirname target-file)or useksh93's>;operator instead ofspongewhich does that automatically (and also doesn't override the target file if the redirected command failed).
– Stéphane Chazelas
yesterday
>;? mind blown.
– glenn jackman
13 hours ago
add a comment |
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
3
down vote
accepted
strace or similar will show the system calls used by sponge, which is probably to write(2) the input read(2) from standard input out to a temporary file, and then to rename(2) that temporary file to the desired output filename when the input ends. The input ends when a read(2) call fails or returns 0 (which indicates end-of-file) at which point sponge can do the rename.
answered yesterday
thrig
23.6k12955
And when therename()fails with EXDEV when/tmpis on a different file system, it ends up copying the data again into the destination file. You can avoid that by settingTMPDIRto$(dirname target-file)or useksh93's>;operator instead ofspongewhich does that automatically (and also doesn't override the target file if the redirected command failed).
– Stéphane Chazelas
yesterday
>;? mind blown.
– glenn jackman
13 hours ago
add a comment |
up vote
3
down vote
accepted
strace or similar will show the system calls used by sponge, which is probably to write(2) the input read(2) from standard input out to a temporary file, and then to rename(2) that temporary file to the desired output filename when the input ends. The input ends when a read(2) call fails or returns 0 (which indicates end-of-file) at which point sponge can do the rename.
answered yesterday
thrig
23.6k12955
And when therename()fails with EXDEV when/tmpis on a different file system, it ends up copying the data again into the destination file. You can avoid that by settingTMPDIRto$(dirname target-file)or useksh93's>;operator instead ofspongewhich does that automatically (and also doesn't override the target file if the redirected command failed).
– Stéphane Chazelas
yesterday
>;? mind blown.
– glenn jackman
13 hours ago
add a comment |
up vote
3
down vote
accepted
up vote
3
down vote
accepted
strace or similar will show the system calls used by sponge, which is probably to write(2) the input read(2) from standard input out to a temporary file, and then to rename(2) that temporary file to the desired output filename when the input ends. The input ends when a read(2) call fails or returns 0 (which indicates end-of-file) at which point sponge can do the rename.
answered yesterday
thrig
23.6k12955
strace or similar will show the system calls used by sponge, which is probably to write(2) the input read(2) from standard input out to a temporary file, and then to rename(2) that temporary file to the desired output filename when the input ends. The input ends when a read(2) call fails or returns 0 (which indicates end-of-file) at which point sponge can do the rename.
answered yesterday
thrig
23.6k12955
edited yesterday
answered yesterday
thrig
23.6k12955
answered yesterday
thrig
23.6k12955
answered yesterday
thrig
23.6k12955
23.6k12955
And when therename()fails with EXDEV when/tmpis on a different file system, it ends up copying the data again into the destination file. You can avoid that by settingTMPDIRto$(dirname target-file)or useksh93's>;operator instead ofspongewhich does that automatically (and also doesn't override the target file if the redirected command failed).
– Stéphane Chazelas
yesterday
>;? mind blown.
– glenn jackman
13 hours ago
add a comment |
And when therename()fails with EXDEV when/tmpis on a different file system, it ends up copying the data again into the destination file. You can avoid that by settingTMPDIRto$(dirname target-file)or useksh93's>;operator instead ofspongewhich does that automatically (and also doesn't override the target file if the redirected command failed).
– Stéphane Chazelas
yesterday
>;? mind blown.
– glenn jackman
13 hours ago
And when the
rename() fails with EXDEV when /tmp is on a different file system, it ends up copying the data again into the destination file. You can avoid that by setting TMPDIR to $(dirname target-file) or use ksh93's >; operator instead of sponge which does that automatically (and also doesn't override the target file if the redirected command failed).– Stéphane Chazelas
yesterday
And when the
rename() fails with EXDEV when /tmp is on a different file system, it ends up copying the data again into the destination file. You can avoid that by setting TMPDIR to $(dirname target-file) or use ksh93's >; operator instead of sponge which does that automatically (and also doesn't override the target file if the redirected command failed).– Stéphane Chazelas
yesterday
>; ? mind blown.– glenn jackman
13 hours ago
>; ? mind blown.– glenn jackman
13 hours ago
add a comment |
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2
What do you mean? The same way every other program knows (e.g.
cat f | wcorcat f | grep fooor whatever), why would you expectspongeto be special?– terdon♦
yesterday