用命令输出替换字符串，每次都不同

Question

I have many files and I want to replace the class names with a UUID. I figured out this

sed -i -r "s/ Class \w(\w|\d)+/ Class C$(python -c 'import uuid;print(uuid.uuid4().hex)')/"

It works fine when the pattern only occurs once in each file. However if the pattern occurs more than once, each occurence is replaced by the same number.

Class1.vb

Public Class Class1
    Public ReadOnly Property P As String = "hello"
End Class

Public Class Class2
    Public ReadOnly Property P As String = "hello"
End Class

$ sed -r "s/ Class \w(\w|\d)+/ Class C$(echo $RANDOM)/" Class1.vb
Public Class C27244
        Public ReadOnly Property P As String = "hello"
End Class

Public Class C27244
        Public ReadOnly Property P As String = "hello"
End Class

I expect the two classes to have different names. How do I fix my script?

Answer 1

$ awk '{gsub(/Class [[:alnum:]]+/, "Class C" int(9999*rand()))} 1' Class1.vb
Public Class C2377
    Public ReadOnly Property P As String = "hello"
End Class

Public Class C5854
    Public ReadOnly Property P As String = "hello"
End Class

The above will give you the same random numbers in the same order each time. If you want different random numbers each time you run the program, use:

awk -v s=$RANDOM 'BEGIN{srand(s)} {gsub(/Class [[:alnum:]]+/, "Class C" int(9999*rand()))} 1' Class1.vb

How it works

• gsub(/Class [[:alnum:]]+/, "Class C" int(9999*rand()))

  This looks for occurrences of the regex Class [[:alnum:]]+ and replaces each one with the concatenation of the string Class C and a four-digit random number calculated from int(9999*rand()) . A new random number is generated for each line.

• 1

  This is awk's cryptic shorthand for print-the-current-line.

Answer 2

More as a proof of concept than a serious alternative: a GNU sed solution.

sed -E -e '/Class \w+/{h;s/.*/bash -c "echo C\\$RANDOM"/;e' \
    -e 'G;s/(.*)\n(.*Class )\w+(.*)/\2\1\3/}' infile

resulting in

Public Class C24276
    Public ReadOnly Property P As String = "hello"
End Class

Public Class C28554
    Public ReadOnly Property P As String = "hello"
End Class

Here is how it works:

/Class \w+/ {                           # If the line matches "Class <name>"
    h                                   # Copy pattern space to hold space
    s/.*/bash -c "echo C\\$RANDOM"/     # Write Bash command into pattern space
    e                                   # Replace pattern space with command output
    G                                   # Append hold space to pattern space
    s/(.*)\n(.*Class )\w+(.*)/\2\1\3/   # Swap class name with random number
}

Remarks:

• This uses GNU extensions: notably the \\w character class and the e command.
  • \\w includes digits , so there is no need for (\\w|\\d) .
• The one-liner version is split into two commands using -e because the e command cannot be followed by anything, or that anything is interpreted as the command.
• The command to be run can't just be echo C$RANDOM because the e command uses sh instead of Bash, and sh might not have $RANDOM (like on Ubuntu, where sh is dash).

• Because the command is in double quotes, the $ in $RANDOM has to be escaped, and because sed does a first pass before the shell sees the command, is has to be escaped twice. Alternatively, I could have used

   s/.*/bash -c '\\''echo C$RANDOM'\\''/ 

  to single quote the command, but that's not very readable either.