Cat, Grep and Cut - Translated to Python

cat, grep and cut - translated to python

You need to have better understanding of the python language and its standard library to translate the expression

cat "$filename": Reads the file cat "$filename" and dumps the content to stdout

|: pipe redirects the stdout from previous command and feeds it to the stdin of the next command

grep "something": Searches the regular expressionsomething plain text data file (if specified) or in the stdin and returns the matching lines.

cut -d'"' -f2: Splits the string with the specific delimiter and indexes/splices particular fields from the resultant list

Python Equivalent

cat "$filename"  | with open("$filename",'r') as fin:        | Read the file Sequentially
                 |     for line in fin:                      |   
-----------------------------------------------------------------------------------
grep 'something' | import re                                 | The python version returns
                 | line = re.findall(r'something', line)[0]  | a list of matches. We are only
                 |                                           | interested in the zero group
-----------------------------------------------------------------------------------
cut -d'"' -f2    | line = line.split('"')[1]                 | Splits the string and selects
                 |                                           | the second field (which is
                 |                                           | index 1 in python)

Combining

import re
with open("filename") as origin_file:
    for line in origin_file:
        line = re.findall(r'something', line)
        if line:
           line = line[0].split('"')[1]
        print line

What is the code equivalent to grep -B in python?

You'll just have to keep a buffer (a list) of the N last lines, then print them when you encounter a match.

context_lines = []
for line in f:
    context_lines.append(line)
    if len(context_lines) > 5:  # Too many lines?
        context_lines.pop(0)  # Pop the first one off.
    if word in line:
        # context_lines already includes the `line` we're looking at
        for ctx_line in context_lines:  
             print(ctx_line)

run linux cat command in python or bash loop

In your python command, you are doing it wrongly , the % count should be inside the os.system() call. Example -

os.system('''cat member.php\?%d* | grep -i '<li class="navbit lastnavbit"><span>' | cut -d'>' -f3 | cut -d'<' -f1  >> users.txt''' % count)

Also, you should iterate till the amount you want.

Use cut and grep to separate data while printing multiple fields

I found what I was looking for in some documentation. Anchor matches!

grep "$week$" file

would output this if $week was 0

asset.14548.extension    0
asset.40795.extension    0

I couldn't find my exact question or a closely similar question with a simple answer, so hopefully it helps the next person scratching their head on this.

parsing results in bash

Without a sample file, it is hard to write a working example. But I see, both values are from the same text file and the same line. Therefore I would use awk to do it:

$ cat text
service1;some_other_text;2.3.4
service2;just_some_text;55.66

$awk -F ";" '{printf "%s:%s\n",  $1, $3}' test 
service1:2.3.4

For a JSON file, it would be easier if you can use jg (e.g. apt-get install jg):

$ cat test.json
[
  {
    "name": "service1",
    "customfield_10090": "1.2.3"
  },
  {
    "name": "service2",
    "customfield_10090": "23.3.2"
  }
]

$jq '.[] | .name + ":" + .customfield_10090' test.json | sed 's/"//g'
service1:1.2.3
service2:23.3.2

The sed is necessary to eliminate the quotes.

Search for list of keywords in python

For a minimal change to get this working, you can change any(keywords) in string_tags to the following:

any(keyword in string_tags for keyword in keywords)

Or an alternative using sets:

keywords = set(['diy','decorate', 'craft', 'home decor', 'food'])

def get_tags(blog_soup):
    tags_html = blog_soup.find('div', attrs = {'style': 'margin-left: 60px; margin-bottom: 15px;'})
    tags = [tag.string for tag in tags_html.findAll('a')]
    if keywords.intersection(tags):
        print url

how to grep everything between single quotes?

Try something like this: sed -n "s#version:\s*'\(.*\)'#\1#p" myfile.txt. This avoids the redundant cat and grep by finding the "version" line and extracting the contents between the single quotes.

Explanation:

the -n flag tells sed not to print lines automatically. We then use the p command at the end of our sed pattern to explicitly print when we've found the version line.

Search for pattern: version:\s*'\(.*\)'

• version:\s* Match "version:" followed by any amount of whitespace
• '\(.*\)' Match a single ', then capture everything until the next '

Replace with: \1; This is the first (and only) capture group above, containing contents between single quotes.

How to concatenate multiple lines of output to one line?

Use tr '\n' ' ' to translate all newline characters to spaces:

$ grep pattern file | tr '\n' ' '

Note: grep reads files, cat concatenates files. Don't cat file | grep!

Edit:

tr can only handle single character translations. You could use awk to change the output record separator like:

$ grep pattern file | awk '{print}' ORS='" '

This would transform:

one
two 
three

to:

one" two" three" 

How can I grep for a string that begins with a dash/hyphen?

Use:

grep -- -X

Documentation

Related: What does a bare double dash mean? (thanks to nutty about natty).

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