How is the wildcard * interpreted as a command?
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I know how * is interpreted in commands like ls for example. But when trying to run * as a command the shell tries to execute the first file or directory in your working directory. Why is this? How does the shell understand *?
bash wildcards
edited Mar 11 at 20:31
Glorfindel
3371511
asked Mar 11 at 19:07
osmakosmak
434
add a comment |
I know how * is interpreted in commands like ls for example. But when trying to run * as a command the shell tries to execute the first file or directory in your working directory. Why is this? How does the shell understand *?
bash wildcards
edited Mar 11 at 20:31
Glorfindel
3371511
asked Mar 11 at 19:07
osmakosmak
434
add a comment |
I know how * is interpreted in commands like ls for example. But when trying to run * as a command the shell tries to execute the first file or directory in your working directory. Why is this? How does the shell understand *?
bash wildcards
edited Mar 11 at 20:31
Glorfindel
3371511
asked Mar 11 at 19:07
osmakosmak
434
I know how * is interpreted in commands like ls for example. But when trying to run * as a command the shell tries to execute the first file or directory in your working directory. Why is this? How does the shell understand *?
bash wildcards
bash wildcards
edited Mar 11 at 20:31
Glorfindel
3371511
asked Mar 11 at 19:07
osmakosmak
434
edited Mar 11 at 20:31
Glorfindel
3371511
asked Mar 11 at 19:07
osmakosmak
434
edited Mar 11 at 20:31
Glorfindel
3371511
edited Mar 11 at 20:31
Glorfindel
3371511
edited Mar 11 at 20:31
Glorfindel
3371511
3371511
asked Mar 11 at 19:07
osmakosmak
434
asked Mar 11 at 19:07
osmakosmak
434
asked Mar 11 at 19:07
osmakosmak
434
434
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
Unlike in some other operating systems, in Unixes, it's the shell that expands filename wildcards. It expands parameter expansions and globs first, then uses the (now) first word as the name for the command to run.
This is also why files named with a leading dash can be troublesome: a glob like * will expand to the file names, and a name starting with a dash may be taken as an option. (The scary example being that a file called -r in the working directory would make rm * remove everything recursively...)
Usually, one wouldn't use * as the first item on any command line, though, so having the first file determine the command to run in that case isn't likely to cause problems.
edited Mar 11 at 22:33
DarkHeart
3,54632441
answered Mar 11 at 19:17
ilkkachuilkkachu
63.3k10104181
1
I think this example misses an important point out, that filename expansion is not subject to further field splitting, unlike parameter expansion, so filenames with spaces are still safe.
– Michael Homer
Mar 11 at 19:31
OK, so I think I misunderstood how the * work in the first place. I thought that it is a common syntax used in Linux commands. But, if I understood your answer correctly, then filename expansion is a shell feature not a command feature. So what happened is that * got replaced by all file or directory names in PWD but when the shell tried executing the first one it produced the error I saw.
– osmak
Mar 11 at 19:42
@osmak, yeah, it's a shell feature on Unixes. Easier that way, so each and every program doesn't have to implement it. Though of course programs likefindknow how to expand similar patterns, too (e.g.file -name "*.txt")
– ilkkachu
Mar 11 at 19:56
@osmak That is a correct understanding.
– Kusalananda♦
Mar 11 at 19:56
2
A file named-ris bad, but one named-rfis even worse.
– Monty Harder
Mar 11 at 21:57
|
show 4 more comments
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1 Answer
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1 Answer
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oldest
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votes
Unlike in some other operating systems, in Unixes, it's the shell that expands filename wildcards. It expands parameter expansions and globs first, then uses the (now) first word as the name for the command to run.
This is also why files named with a leading dash can be troublesome: a glob like * will expand to the file names, and a name starting with a dash may be taken as an option. (The scary example being that a file called -r in the working directory would make rm * remove everything recursively...)
Usually, one wouldn't use * as the first item on any command line, though, so having the first file determine the command to run in that case isn't likely to cause problems.
edited Mar 11 at 22:33
DarkHeart
3,54632441
answered Mar 11 at 19:17
ilkkachuilkkachu
63.3k10104181
1
I think this example misses an important point out, that filename expansion is not subject to further field splitting, unlike parameter expansion, so filenames with spaces are still safe.
– Michael Homer
Mar 11 at 19:31
OK, so I think I misunderstood how the * work in the first place. I thought that it is a common syntax used in Linux commands. But, if I understood your answer correctly, then filename expansion is a shell feature not a command feature. So what happened is that * got replaced by all file or directory names in PWD but when the shell tried executing the first one it produced the error I saw.
– osmak
Mar 11 at 19:42
@osmak, yeah, it's a shell feature on Unixes. Easier that way, so each and every program doesn't have to implement it. Though of course programs likefindknow how to expand similar patterns, too (e.g.file -name "*.txt")
– ilkkachu
Mar 11 at 19:56
@osmak That is a correct understanding.
– Kusalananda♦
Mar 11 at 19:56
2
A file named-ris bad, but one named-rfis even worse.
– Monty Harder
Mar 11 at 21:57
|
show 4 more comments
Unlike in some other operating systems, in Unixes, it's the shell that expands filename wildcards. It expands parameter expansions and globs first, then uses the (now) first word as the name for the command to run.
This is also why files named with a leading dash can be troublesome: a glob like * will expand to the file names, and a name starting with a dash may be taken as an option. (The scary example being that a file called -r in the working directory would make rm * remove everything recursively...)
Usually, one wouldn't use * as the first item on any command line, though, so having the first file determine the command to run in that case isn't likely to cause problems.
edited Mar 11 at 22:33
DarkHeart
3,54632441
answered Mar 11 at 19:17
ilkkachuilkkachu
63.3k10104181
1
I think this example misses an important point out, that filename expansion is not subject to further field splitting, unlike parameter expansion, so filenames with spaces are still safe.
– Michael Homer
Mar 11 at 19:31
OK, so I think I misunderstood how the * work in the first place. I thought that it is a common syntax used in Linux commands. But, if I understood your answer correctly, then filename expansion is a shell feature not a command feature. So what happened is that * got replaced by all file or directory names in PWD but when the shell tried executing the first one it produced the error I saw.
– osmak
Mar 11 at 19:42
@osmak, yeah, it's a shell feature on Unixes. Easier that way, so each and every program doesn't have to implement it. Though of course programs likefindknow how to expand similar patterns, too (e.g.file -name "*.txt")
– ilkkachu
Mar 11 at 19:56
@osmak That is a correct understanding.
– Kusalananda♦
Mar 11 at 19:56
2
A file named-ris bad, but one named-rfis even worse.
– Monty Harder
Mar 11 at 21:57
|
show 4 more comments
Unlike in some other operating systems, in Unixes, it's the shell that expands filename wildcards. It expands parameter expansions and globs first, then uses the (now) first word as the name for the command to run.
This is also why files named with a leading dash can be troublesome: a glob like * will expand to the file names, and a name starting with a dash may be taken as an option. (The scary example being that a file called -r in the working directory would make rm * remove everything recursively...)
Usually, one wouldn't use * as the first item on any command line, though, so having the first file determine the command to run in that case isn't likely to cause problems.
edited Mar 11 at 22:33
DarkHeart
3,54632441
answered Mar 11 at 19:17
ilkkachuilkkachu
63.3k10104181
Unlike in some other operating systems, in Unixes, it's the shell that expands filename wildcards. It expands parameter expansions and globs first, then uses the (now) first word as the name for the command to run.
This is also why files named with a leading dash can be troublesome: a glob like * will expand to the file names, and a name starting with a dash may be taken as an option. (The scary example being that a file called -r in the working directory would make rm * remove everything recursively...)
Usually, one wouldn't use * as the first item on any command line, though, so having the first file determine the command to run in that case isn't likely to cause problems.
edited Mar 11 at 22:33
DarkHeart
3,54632441
answered Mar 11 at 19:17
ilkkachuilkkachu
63.3k10104181
edited Mar 11 at 22:33
DarkHeart
3,54632441
edited Mar 11 at 22:33
DarkHeart
3,54632441
edited Mar 11 at 22:33
DarkHeart
3,54632441
3,54632441
answered Mar 11 at 19:17
ilkkachuilkkachu
63.3k10104181
answered Mar 11 at 19:17
ilkkachuilkkachu
63.3k10104181
answered Mar 11 at 19:17
ilkkachuilkkachu
63.3k10104181
63.3k10104181
1
I think this example misses an important point out, that filename expansion is not subject to further field splitting, unlike parameter expansion, so filenames with spaces are still safe.
– Michael Homer
Mar 11 at 19:31
OK, so I think I misunderstood how the * work in the first place. I thought that it is a common syntax used in Linux commands. But, if I understood your answer correctly, then filename expansion is a shell feature not a command feature. So what happened is that * got replaced by all file or directory names in PWD but when the shell tried executing the first one it produced the error I saw.
– osmak
Mar 11 at 19:42
@osmak, yeah, it's a shell feature on Unixes. Easier that way, so each and every program doesn't have to implement it. Though of course programs likefindknow how to expand similar patterns, too (e.g.file -name "*.txt")
– ilkkachu
Mar 11 at 19:56
@osmak That is a correct understanding.
– Kusalananda♦
Mar 11 at 19:56
2
A file named-ris bad, but one named-rfis even worse.
– Monty Harder
Mar 11 at 21:57
|
show 4 more comments
1
I think this example misses an important point out, that filename expansion is not subject to further field splitting, unlike parameter expansion, so filenames with spaces are still safe.
– Michael Homer
Mar 11 at 19:31
OK, so I think I misunderstood how the * work in the first place. I thought that it is a common syntax used in Linux commands. But, if I understood your answer correctly, then filename expansion is a shell feature not a command feature. So what happened is that * got replaced by all file or directory names in PWD but when the shell tried executing the first one it produced the error I saw.
– osmak
Mar 11 at 19:42
@osmak, yeah, it's a shell feature on Unixes. Easier that way, so each and every program doesn't have to implement it. Though of course programs likefindknow how to expand similar patterns, too (e.g.file -name "*.txt")
– ilkkachu
Mar 11 at 19:56
@osmak That is a correct understanding.
– Kusalananda♦
Mar 11 at 19:56
2
A file named-ris bad, but one named-rfis even worse.
– Monty Harder
Mar 11 at 21:57
1
1
I think this example misses an important point out, that filename expansion is not subject to further field splitting, unlike parameter expansion, so filenames with spaces are still safe.
– Michael Homer
Mar 11 at 19:31
I think this example misses an important point out, that filename expansion is not subject to further field splitting, unlike parameter expansion, so filenames with spaces are still safe.
– Michael Homer
Mar 11 at 19:31
OK, so I think I misunderstood how the * work in the first place. I thought that it is a common syntax used in Linux commands. But, if I understood your answer correctly, then filename expansion is a shell feature not a command feature. So what happened is that * got replaced by all file or directory names in PWD but when the shell tried executing the first one it produced the error I saw.
– osmak
Mar 11 at 19:42
OK, so I think I misunderstood how the * work in the first place. I thought that it is a common syntax used in Linux commands. But, if I understood your answer correctly, then filename expansion is a shell feature not a command feature. So what happened is that * got replaced by all file or directory names in PWD but when the shell tried executing the first one it produced the error I saw.
– osmak
Mar 11 at 19:42
@osmak, yeah, it's a shell feature on Unixes. Easier that way, so each and every program doesn't have to implement it. Though of course programs like
find know how to expand similar patterns, too (e.g. file -name "*.txt")– ilkkachu
Mar 11 at 19:56
@osmak, yeah, it's a shell feature on Unixes. Easier that way, so each and every program doesn't have to implement it. Though of course programs like
find know how to expand similar patterns, too (e.g. file -name "*.txt")– ilkkachu
Mar 11 at 19:56
@osmak That is a correct understanding.
– Kusalananda♦
Mar 11 at 19:56
@osmak That is a correct understanding.
– Kusalananda♦
Mar 11 at 19:56
2
2
A file named
-r is bad, but one named -rf is even worse.– Monty Harder
Mar 11 at 21:57
A file named
-r is bad, but one named -rf is even worse.– Monty Harder
Mar 11 at 21:57
|
show 4 more comments
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