Reordering strings in linux

Question

How can I change lines around using the command line?
e.g. I have these lines:

    Acct-Status-Type = Start
    User-Name = "37XXXXXXX"
    Event-Timestamp = "Apr 12 2013 15:56:55 AMT"

I need to change the order to this:

    Event-Timestamp = "Apr 12 2013 15:56:55 AMT"
    User-Name = "37XXXXXXX"
    Acct-Status-Type = Start

I need to do this by one command, sed, awk, perl or something like that.

Answer 1

Depends on where, how often, why etc you do this, but it wouldn't hurt to put it in a script.

Anyhow you could do something like this to print in defined order. By this approach you can also choose to only print a selected few. E.g. only 1 and 3:

One liner:

awk -v order=312 \
'/^/{ln[NR]=$0}END{split(order,a,"");
 for(i in a)printf("%s\n",ln[a[i]]);}' \
 sample.txt

Or more easy to read:

/^/{
    ln[NR] = $0
}
END{
    split(order,a,"");

    for(i in a)
        printf("%s\n",ln[a[i]]);
}

For the split you could add some delimiter if more then 9 lines.

E.g.:

split(order,a,"-");
# and call by:
awk -v order=3-13-21-12-2 ...

Or to support multiple:

if (order ~ /-/)       split(order, a, "-"); # order has "-", split
else if (order ~ /\./) split(order, a, "."); # order has ".", split
else if (order ~/:/)   split(order, a, ":"); # order has ":", split
else                   split(order, a, "");  # none presume numbers split all

You could also choose to match lines as in:

BEGIN {
    i = 0;
}
/^\s*Acct-Status-Type/ {ln[++i] = $0 }
/^\s*User-Name/ {ln[++i] = $0 }
/^\s*Event-Timestamp/ {ln[++i] = $0 }
END {
    if (order ~ /-/)  split(order, a, "-");
    else if (order ~ /\./) split(order, a, ".");
    else if (order ~/:/) split(order, a, ":");
    else split(order, a, "")
    for (i in a)
        printf("%s\n", ln[a[i]]);
}

---

Edit:

For last sample this would probably be better. (Also updated the split):

/^\s*Acct-Status-Type/ {ln[1] = $0 }
/^\s*User-Name/ {ln[2] = $0 }
/^\s*Event-Timestamp/ {ln[3] = $0 }
END {
    if (split(order, a, "-|:|,| |\\.") == 1) # Space require quoting of arg.
        split(order, a, "")
    for (i in a)
        printf("%s\n", ln[a[i]]);
}

Answer 2

With Python and the name of the file as the commandline parameter to the program:

import sys
with open(sys.argv[1]) as fp:
    for line in fp.readlines()[::-1]:
        sys.stdout.write(line)

or writing it back to that file:

import sys
with open(sys.argv[1]) as fp:
    lines = fp.readlines()
with open(sys.argv[1], 'w') as fp:
    for line in lines[::-1]:
        fp.write(line)

or as a filter from stdin to stdout:

lines = sys.stdin.readlines()
for line in lines[::-1]:
    sys.stdout.write(line)