How is the wildcard * interpreted as a command?












2















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







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    2















    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







    share|improve this question









    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.























      2












      2








      2








      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







      share|improve this question









      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






      share|improve this question









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      osmak is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.











      share|improve this question









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      share|improve this question




      share|improve this question








      edited 5 hours ago









      Glorfindel

      2991411




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      asked 7 hours ago









      osmakosmak

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          1 Answer
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          7














          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.






          share|improve this answer





















          • 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
            6 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
            6 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
            6 hours ago











          • @osmak That is a correct understanding.

            – Kusalananda
            6 hours ago






          • 2





            A file named -r is bad, but one named -rf is even worse.

            – Monty Harder
            4 hours ago











          Your Answer








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          1 Answer
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          active

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          1 Answer
          1






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes









          7














          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.






          share|improve this answer





















          • 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
            6 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
            6 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
            6 hours ago











          • @osmak That is a correct understanding.

            – Kusalananda
            6 hours ago






          • 2





            A file named -r is bad, but one named -rf is even worse.

            – Monty Harder
            4 hours ago
















          7














          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.






          share|improve this answer





















          • 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
            6 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
            6 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
            6 hours ago











          • @osmak That is a correct understanding.

            – Kusalananda
            6 hours ago






          • 2





            A file named -r is bad, but one named -rf is even worse.

            – Monty Harder
            4 hours ago














          7












          7








          7







          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.






          share|improve this answer















          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.







          share|improve this answer














          share|improve this answer



          share|improve this answer








          edited 3 hours ago









          DarkHeart

          3,52632340




          3,52632340










          answered 6 hours ago









          ilkkachuilkkachu

          60.9k1098174




          60.9k1098174








          • 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
            6 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
            6 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
            6 hours ago











          • @osmak That is a correct understanding.

            – Kusalananda
            6 hours ago






          • 2





            A file named -r is bad, but one named -rf is even worse.

            – Monty Harder
            4 hours ago














          • 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
            6 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
            6 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
            6 hours ago











          • @osmak That is a correct understanding.

            – Kusalananda
            6 hours ago






          • 2





            A file named -r is bad, but one named -rf is even worse.

            – Monty Harder
            4 hours ago








          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
          6 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
          6 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
          6 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
          6 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
          6 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
          6 hours ago













          @osmak That is a correct understanding.

          – Kusalananda
          6 hours ago





          @osmak That is a correct understanding.

          – Kusalananda
          6 hours ago




          2




          2





          A file named -r is bad, but one named -rf is even worse.

          – Monty Harder
          4 hours ago





          A file named -r is bad, but one named -rf is even worse.

          – Monty Harder
          4 hours ago










          osmak is a new contributor. Be nice, and check out our Code of Conduct.










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