awk: Built-in FILENAME variable on empty file
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Why does awk's FILENAME variable return nothing when input is a empty file? Does this means awk doesn't open that file? If doesn't open how knows it's empty, or if it's open why doesn't return filename then?
I read this post, but there not explained why below should work.
awk 'BEGINFILEprint FILENAME1' filename
and below doesn't.
awk 'print FILENAME' filename #or
awk 'BEGINprint FILENAME' filename
awk
asked Oct 21 '17 at 13:30
αғsýιη
15.6k92563
add a comment |Â
up vote
4
down vote
favorite
1
Why does awk's FILENAME variable return nothing when input is a empty file? Does this means awk doesn't open that file? If doesn't open how knows it's empty, or if it's open why doesn't return filename then?
I read this post, but there not explained why below should work.
awk 'BEGINFILEprint FILENAME1' filename
and below doesn't.
awk 'print FILENAME' filename #or
awk 'BEGINprint FILENAME' filename
awk
asked Oct 21 '17 at 13:30
αғsýιη
15.6k92563
A good question. See the following and seeFILENAMEpagagraph: kirste.userpage.fu-berlin.de/chemnet/use/info/gawk/gawk_11.html I quoteInside a BEGIN rule, the value of FILENAME is "", since there are no input files being processed yet
– Valentin B
Oct 21 '17 at 13:50
Thanks, there I can see mentioned "FILENAME is "", since there are no input files being processed yet". With considering this apart of if it's in BEGIN or not, means FILENAME set when not in BEGIN and a input file specified not depending on "if file has a field" as below Nd64's answer points and as I tested it depends on if a file has a field but not documented.
– Î±Ò“sýιη
Oct 21 '17 at 13:55
To elaborate on my previous comment. Since theBEGINstatement is ran before anything, at that momentFILENAMEor any other built in variable likeNRorNFis undefined/empty.
– Valentin B
Oct 21 '17 at 13:55
add a comment |Â
up vote
4
down vote
favorite
1
up vote
4
down vote
favorite
1
1
Why does awk's FILENAME variable return nothing when input is a empty file? Does this means awk doesn't open that file? If doesn't open how knows it's empty, or if it's open why doesn't return filename then?
I read this post, but there not explained why below should work.
awk 'BEGINFILEprint FILENAME1' filename
and below doesn't.
awk 'print FILENAME' filename #or
awk 'BEGINprint FILENAME' filename
awk
asked Oct 21 '17 at 13:30
αғsýιη
15.6k92563
Why does awk's FILENAME variable return nothing when input is a empty file? Does this means awk doesn't open that file? If doesn't open how knows it's empty, or if it's open why doesn't return filename then?
I read this post, but there not explained why below should work.
awk 'BEGINFILEprint FILENAME1' filename
and below doesn't.
awk 'print FILENAME' filename #or
awk 'BEGINprint FILENAME' filename
awk
asked Oct 21 '17 at 13:30
αғsýιη
15.6k92563
edited Oct 21 '17 at 13:36
asked Oct 21 '17 at 13:30
αғsýιη
15.6k92563
asked Oct 21 '17 at 13:30
αғsýιη
15.6k92563
asked Oct 21 '17 at 13:30
αғsýιη
15.6k92563
15.6k92563
A good question. See the following and seeFILENAMEpagagraph: kirste.userpage.fu-berlin.de/chemnet/use/info/gawk/gawk_11.html I quoteInside a BEGIN rule, the value of FILENAME is "", since there are no input files being processed yet
– Valentin B
Oct 21 '17 at 13:50
Thanks, there I can see mentioned "FILENAME is "", since there are no input files being processed yet". With considering this apart of if it's in BEGIN or not, means FILENAME set when not in BEGIN and a input file specified not depending on "if file has a field" as below Nd64's answer points and as I tested it depends on if a file has a field but not documented.
– Î±Ò“sýιη
Oct 21 '17 at 13:55
To elaborate on my previous comment. Since theBEGINstatement is ran before anything, at that momentFILENAMEor any other built in variable likeNRorNFis undefined/empty.
– Valentin B
Oct 21 '17 at 13:55
add a comment |Â
A good question. See the following and seeFILENAMEpagagraph: kirste.userpage.fu-berlin.de/chemnet/use/info/gawk/gawk_11.html I quoteInside a BEGIN rule, the value of FILENAME is "", since there are no input files being processed yet
– Valentin B
Oct 21 '17 at 13:50
Thanks, there I can see mentioned "FILENAME is "", since there are no input files being processed yet". With considering this apart of if it's in BEGIN or not, means FILENAME set when not in BEGIN and a input file specified not depending on "if file has a field" as below Nd64's answer points and as I tested it depends on if a file has a field but not documented.
– Î±Ò“sýιη
Oct 21 '17 at 13:55
To elaborate on my previous comment. Since theBEGINstatement is ran before anything, at that momentFILENAMEor any other built in variable likeNRorNFis undefined/empty.
– Valentin B
Oct 21 '17 at 13:55
A good question. See the following and see
FILENAME pagagraph: kirste.userpage.fu-berlin.de/chemnet/use/info/gawk/gawk_11.html I quote Inside a BEGIN rule, the value of FILENAME is "", since there are no input files being processed yet– Valentin B
Oct 21 '17 at 13:50
A good question. See the following and see
FILENAME pagagraph: kirste.userpage.fu-berlin.de/chemnet/use/info/gawk/gawk_11.html I quote Inside a BEGIN rule, the value of FILENAME is "", since there are no input files being processed yet– Valentin B
Oct 21 '17 at 13:50
Thanks, there I can see mentioned "FILENAME is "", since there are no input files being processed yet". With considering this apart of if it's in BEGIN or not, means FILENAME set when not in BEGIN and a input file specified not depending on "if file has a field" as below Nd64's answer points and as I tested it depends on if a file has a field but not documented.
– Î±Ò“sýιη
Oct 21 '17 at 13:55
Thanks, there I can see mentioned "FILENAME is "", since there are no input files being processed yet". With considering this apart of if it's in BEGIN or not, means FILENAME set when not in BEGIN and a input file specified not depending on "if file has a field" as below Nd64's answer points and as I tested it depends on if a file has a field but not documented.
– Î±Ò“sýιη
Oct 21 '17 at 13:55
To elaborate on my previous comment. Since the
BEGIN statement is ran before anything, at that moment FILENAME or any other built in variable like NR or NF is undefined/empty.– Valentin B
Oct 21 '17 at 13:55
To elaborate on my previous comment. Since the
BEGIN statement is ran before anything, at that moment FILENAME or any other built in variable like NR or NF is undefined/empty.– Valentin B
Oct 21 '17 at 13:55
add a comment |Â
1 Answer
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From the awk manual:
FILENAME A pathname of the current input file.
Inside a BEGIN action the value is undefined. (...)
I think this is the explanation. Until a field is processed the value of FILENAME is undefined. Since no field is processed in case of an empty file the variable stays uninitialised.
answered Oct 21 '17 at 13:36
Ned64
2,44911035
thanks, this "Until a field is processed the value of FILENAME is undefined" should be updated inawk's man page at least.
– Î±Ò“sýιη
Oct 21 '17 at 14:00
Agree! By the way, I checked the source and could not quickly see why it should be uninitialised... Well, we have seen that apparently it is so.
– Ned64
Oct 21 '17 at 17:40
add a comment |Â
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
5
down vote
accepted
From the awk manual:
FILENAME A pathname of the current input file.
Inside a BEGIN action the value is undefined. (...)
I think this is the explanation. Until a field is processed the value of FILENAME is undefined. Since no field is processed in case of an empty file the variable stays uninitialised.
answered Oct 21 '17 at 13:36
Ned64
2,44911035
thanks, this "Until a field is processed the value of FILENAME is undefined" should be updated inawk's man page at least.
– Î±Ò“sýιη
Oct 21 '17 at 14:00
Agree! By the way, I checked the source and could not quickly see why it should be uninitialised... Well, we have seen that apparently it is so.
– Ned64
Oct 21 '17 at 17:40
add a comment |Â
up vote
5
down vote
accepted
From the awk manual:
FILENAME A pathname of the current input file.
Inside a BEGIN action the value is undefined. (...)
I think this is the explanation. Until a field is processed the value of FILENAME is undefined. Since no field is processed in case of an empty file the variable stays uninitialised.
answered Oct 21 '17 at 13:36
Ned64
2,44911035
thanks, this "Until a field is processed the value of FILENAME is undefined" should be updated inawk's man page at least.
– Î±Ò“sýιη
Oct 21 '17 at 14:00
Agree! By the way, I checked the source and could not quickly see why it should be uninitialised... Well, we have seen that apparently it is so.
– Ned64
Oct 21 '17 at 17:40
add a comment |Â
up vote
5
down vote
accepted
up vote
5
down vote
accepted
From the awk manual:
FILENAME A pathname of the current input file.
Inside a BEGIN action the value is undefined. (...)
I think this is the explanation. Until a field is processed the value of FILENAME is undefined. Since no field is processed in case of an empty file the variable stays uninitialised.
answered Oct 21 '17 at 13:36
Ned64
2,44911035
From the awk manual:
FILENAME A pathname of the current input file.
Inside a BEGIN action the value is undefined. (...)
I think this is the explanation. Until a field is processed the value of FILENAME is undefined. Since no field is processed in case of an empty file the variable stays uninitialised.
answered Oct 21 '17 at 13:36
Ned64
2,44911035
answered Oct 21 '17 at 13:36
Ned64
2,44911035
answered Oct 21 '17 at 13:36
Ned64
2,44911035
answered Oct 21 '17 at 13:36
Ned64
2,44911035
2,44911035
thanks, this "Until a field is processed the value of FILENAME is undefined" should be updated inawk's man page at least.
– Î±Ò“sýιη
Oct 21 '17 at 14:00
Agree! By the way, I checked the source and could not quickly see why it should be uninitialised... Well, we have seen that apparently it is so.
– Ned64
Oct 21 '17 at 17:40
add a comment |Â
thanks, this "Until a field is processed the value of FILENAME is undefined" should be updated inawk's man page at least.
– Î±Ò“sýιη
Oct 21 '17 at 14:00
Agree! By the way, I checked the source and could not quickly see why it should be uninitialised... Well, we have seen that apparently it is so.
– Ned64
Oct 21 '17 at 17:40
thanks, this "Until a field is processed the value of FILENAME is undefined" should be updated in
awk's man page at least.– Î±Ò“sýιη
Oct 21 '17 at 14:00
thanks, this "Until a field is processed the value of FILENAME is undefined" should be updated in
awk's man page at least.– Î±Ò“sýιη
Oct 21 '17 at 14:00
Agree! By the way, I checked the source and could not quickly see why it should be uninitialised... Well, we have seen that apparently it is so.
– Ned64
Oct 21 '17 at 17:40
Agree! By the way, I checked the source and could not quickly see why it should be uninitialised... Well, we have seen that apparently it is so.
– Ned64
Oct 21 '17 at 17:40
add a comment |Â
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A good question. See the following and see
FILENAMEpagagraph: kirste.userpage.fu-berlin.de/chemnet/use/info/gawk/gawk_11.html I quoteInside a BEGIN rule, the value of FILENAME is "", since there are no input files being processed yet– Valentin B
Oct 21 '17 at 13:50
Thanks, there I can see mentioned "FILENAME is "", since there are no input files being processed yet". With considering this apart of if it's in BEGIN or not, means FILENAME set when not in BEGIN and a input file specified not depending on "if file has a field" as below Nd64's answer points and as I tested it depends on if a file has a field but not documented.
– Î±Ò“sýιη
Oct 21 '17 at 13:55
To elaborate on my previous comment. Since the
BEGINstatement is ran before anything, at that momentFILENAMEor any other built in variable likeNRorNFis undefined/empty.– Valentin B
Oct 21 '17 at 13:55