Question

I want to run a shell script with this usage:

./run A.txt B.xml

A.txt contain some statistic:

Accesses = 1
Hits = 2
Misses = 3
Evictions = 4
Retries = 5

B.xml looks like:

<stat name="total_accesses" value="0"/>
<stat name="total_misses" value="0"/>
<stat name="conflicts" value="0"/>  

I want to replace some stats in B.xml from A.txt. For example, I want to

1- find "Accesses" in A.txt
2- find "total_accesses" in B.xml
3- replace 0 with 1
1- find "Misses" in A.txt
2- find "total_misses" in B.xml
3- replace 0 with 3

So B.xml will look like:

<stat name="total_accesses" value="1"/>
<stat name="total_misses" value="3"/>
<stat name="conflicts" value="0"/>  

I want to do that with shell “sed” command. However I find it quite complex as the regexp is hard to understand.

Does “sed” help me in this problem or I have to find another way?

Answer 1

It might be a bit heavy-weight for such a simple case, but here’s a Python script that does the job:

#!/usr/bin/env python
import sys
import xml.etree.ElementTree as etree

# read A.txt; fill stats
stats = {}
for line in open(sys.argv[1]):
    if line.strip():
        name, _, count = line.partition('=')
        stats["total_"+name.lower().strip()] = count.strip()

# read B.xml; fix to make it a valid xml; replace stat[@value]
root = etree.fromstring("<root>%s</root>" % open(sys.argv[2]).read())
for s in root:
    if s.get('name') in stats:
        s.set('value', stats[s.get('name')])
    print etree.tostring(s),

Example

$ python fill-xml-template.py A.txt B.xml 
<stat name="total_accesses" value="1" />
<stat name="total_misses" value="3" />
<stat name="conflicts" value="0" /> 

To process input files incrementally or to makes changes inplace you could use the following:

#!/usr/bin/env python
import fileinput
import sys
import xml.etree.ElementTree as etree

try: sys.argv.remove('-i')
except ValueError: 
    inplace = False
else: inplace = True # make changes inplace if `-i` option is specified

# read A.txt; fill stats
stats = {}
for line in open(sys.argv.pop(1)):
    if line.strip():
        name, _, count = line.partition('=')
        stats["total_"+name.lower().strip()] = count.strip()

# read input; replace stat[@value]
for line in fileinput.input(inplace=inplace):
    s = etree.fromstring(line)
    if s.get('name') in stats:
        s.set('value', stats[s.get('name')])
    print etree.tostring(s)

Example

$ python fill-xml-template.py A.txt B.xml -i

It can read from stdin or process several files:

$ cat B.xml | python fill-xml-template.py A.txt
<stat name="total_accesses" value="1" />
<stat name="total_misses" value="3" />
<stat name="conflicts" value="0" />