Executing simple command

[magicant]

• Word expansion
• Redirections (common part) Minimum redirection semantics #86
• Assignments (common part) Assignment with absent target #81
• Implementing command search #54

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• Absent target (word expansion resulting in zero fields)
  • Performing redirections in a subshell 26f19ef
  • Applying assignments to the current shell environment Assignment with absent target #81
  • Return the exit status of the last executed command substitution #104
• Invoking a built-in
  • Applying redirections to the built-in a4ae105
  • Applying assignments to the current shell environment (special built-in only) e127ccf
  • Exporting assignments in a temporary context (regular built-in only) 3bc72b5
  • Invoking the built-in body
• Invoking a function
  • Applying redirections to the function d46dd72
  • Exporting assignments in a temporary context Perform assignments in simple command invoking function #97 Assign variables to volatile context in function invocation #99
  • Executing functions #77
• Invoking an external utility
  • Applying redirections to the utility Minimum redirection semantics #86
  • Exporting assignments to the utility d8fe8f7
  • Executing external commands #59
• Target not found
  • Performing the same action as invoking an external utility (*) 4fc393c
• Handling errors (error message and exit status)
  • Target not found 4fc393c
  • Expansion errors b536888 feb591b
  • Redirection errors Minimum redirection semantics #86
  • Assignment errors Assignment with absent target #81

(*) If the command name contains a slash, the command search is skipped, so the shell has no idea whether the command name actually names an existing executable file. That means redirections and assignments are performed even though the external utility invocation is going to fail later. The behavior for command names not containing a slash should be consistent with that.

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Bugs:

• Redirect and assign before forking in simple command #100

[magicant]

Road map for implementing redirection

• < redirection for external utility in simple command
  • Expanding the operand and opening a file
    • System::open
• Applying redirections to built-ins
  • Temporary redirection context / unwinding of redirection
• Applying redirections to functions
• > and other kinds of redirections

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What if redirection is overwritten while executing a function or built-in?

exec 3<file1
f() { exec 3<file2; }
f 3<file3
cat <&3
# Many existing shells (bash, dash, ksh, mksh, zsh, and yash) print "file1"

exec 3<file1
eval 'exec 3<file2' 3<file3
cat <&3
# Many existing shells (bash, dash, ksh, mksh, zsh, and yash) print "file1"