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How is the wildcard * interpreted as a command?
2019 Community Moderator ElectionWorking of the [0-9]Execute command within variableInternal expansion with the find command and wildcard characterCan a bash script tell what directory the user is when they run the script?Selecting non-existent files with wildcard/regexFind wildcard search not working in /etcPurpose of '&& bash' in a command (not the '&&' part, the 'bash' part)Why does a 'sudo -i' login shell break a here-doc command string argument?Bash script copy file to user's (wildcard) home dirBash wget with variables and wildcard
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 1 hour ago
Glorfindel
2971411
asked 2 hours ago
osmakosmak
83
New contributor
osmak is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
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 1 hour ago
Glorfindel
2971411
asked 2 hours ago
osmakosmak
83
New contributor
osmak is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
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 1 hour ago
Glorfindel
2971411
asked 2 hours ago
osmakosmak
83
New contributor
osmak is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
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 1 hour ago
Glorfindel
2971411
asked 2 hours ago
osmakosmak
83
New contributor
osmak is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 1 hour ago
Glorfindel
2971411
asked 2 hours ago
osmakosmak
83
New contributor
osmak is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 1 hour ago
Glorfindel
2971411
edited 1 hour ago
Glorfindel
2971411
edited 1 hour ago
Glorfindel
2971411
2971411
asked 2 hours ago
osmakosmak
83
New contributor
osmak is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 2 hours ago
osmakosmak
83
asked 2 hours ago
osmakosmak
83
83
New contributor
osmak is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
osmak is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
osmak is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
add a comment |
1 Answer
1
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oldest
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That's quite simple, actually. 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.
answered 2 hours ago
ilkkachuilkkachu
60.9k1098174
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
2 hours ago
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
2 hours ago
@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
2 hours ago
@osmak That is a correct understanding.
– Kusalananda
2 hours ago
1
A file named-ris bad, but one named-rfis even worse.
– Monty Harder
9 mins ago
|
show 4 more comments
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1 Answer
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1 Answer
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votes
That's quite simple, actually. 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.
answered 2 hours ago
ilkkachuilkkachu
60.9k1098174
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
2 hours ago
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
2 hours ago
@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
2 hours ago
@osmak That is a correct understanding.
– Kusalananda
2 hours ago
1
A file named-ris bad, but one named-rfis even worse.
– Monty Harder
9 mins ago
|
show 4 more comments
That's quite simple, actually. 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.
answered 2 hours ago
ilkkachuilkkachu
60.9k1098174
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
2 hours ago
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
2 hours ago
@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
2 hours ago
@osmak That is a correct understanding.
– Kusalananda
2 hours ago
1
A file named-ris bad, but one named-rfis even worse.
– Monty Harder
9 mins ago
|
show 4 more comments
That's quite simple, actually. 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.
answered 2 hours ago
ilkkachuilkkachu
60.9k1098174
That's quite simple, actually. 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.
answered 2 hours ago
ilkkachuilkkachu
60.9k1098174
edited 1 hour ago
answered 2 hours ago
ilkkachuilkkachu
60.9k1098174
answered 2 hours ago
ilkkachuilkkachu
60.9k1098174
answered 2 hours ago
ilkkachuilkkachu
60.9k1098174
60.9k1098174
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
2 hours ago
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
2 hours ago
@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
2 hours ago
@osmak That is a correct understanding.
– Kusalananda
2 hours ago
1
A file named-ris bad, but one named-rfis even worse.
– Monty Harder
9 mins ago
|
show 4 more comments
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
2 hours ago
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
2 hours ago
@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
2 hours ago
@osmak That is a correct understanding.
– Kusalananda
2 hours ago
1
A file named-ris bad, but one named-rfis even worse.
– Monty Harder
9 mins ago
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
2 hours ago
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
2 hours ago
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
2 hours ago
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
2 hours ago
@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
2 hours ago
@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
2 hours ago
@osmak That is a correct understanding.
– Kusalananda
2 hours ago
@osmak That is a correct understanding.
– Kusalananda
2 hours ago
1
1
A file named
-r is bad, but one named -rf is even worse.– Monty Harder
9 mins ago
A file named
-r is bad, but one named -rf is even worse.– Monty Harder
9 mins ago
|
show 4 more comments
osmak is a new contributor. Be nice, and check out our Code of Conduct.
osmak is a new contributor. Be nice, and check out our Code of Conduct.
osmak is a new contributor. Be nice, and check out our Code of Conduct.
osmak is a new contributor. Be nice, and check out our Code of Conduct.
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