unix oneliner 1

unixoneliner-1

=> for i in {15..30}; do; pring "Hour:Minute = 16:$i \n" | zgrep 16:$i: access.log | grep -i "s500" cut -d " " -f4 | sort | uniq | print "\n"; done
=> grep -i -e "string1" -e "string2" -e "string3" finename
=> grep -i -e "string1\|string2\|string3"
=> for i in {01,02,05}; do; zgrep s500 $i/access-logfile | grep -i searchString; done | awk '{print $15}' | sort | uniq -c
=> for i in `cat filename`; do; ping -c3 $i; done
=> perl -e 's/(service)(.*?)(family)/$3$2$1/g'

Remove new line character and/or adding a new space:
Mon
Tue
Wed
Thu
Fri
Sat
Sun

Either of the following commands can be used to delete new lines using the tr utility.
tr -d '\n' < days.txt
cat days.txt | tr -d '\n'

While the new line characters can be replaced with spaces using the tr program as follows.
tr '\n' ' ' < days.txt
cat days.txt | tr '\n' ' '

awk — remove new line characters with awk or gawk
Either of the following commands can be used to delete new lines using awk or gawk.
awk '{ printf "%s", $0 }' days.txt
cat days.txt | awk '{ printf "%s", $0 }'

While the new line characters can be replaced with spaces using either of the following commands.
awk '{ printf "%s ", $0 }' days.txt
cat days.txt | awk '{ printf "%s ", $0 }'

Please be careful when using printf's: never pass any unvalidated inputs to printf as a format string as it is a security risk. That is, use: { printf "%s ", $0 } but not: { printf $0 }.
perl — remove new line characters with perl
Either of the following commands can be used to delete new lines using perl.
perl -e 'while (<>) { chomp; print; }; exit;' days.txt
cat days.txt | perl -e 'while (<>) { chomp; print; }; exit;'

While the new line characters can be replaced with spaces using either of the following commands.
perl -e 'while (<>) { chomp; print; print " "; }; exit;' days.txt
cat days.txt | perl -e 'while (<>) { chomp; print; print " "; }; exit;'

Here are some more perl examples:
perl -p -e 's/\s+$/ /g' days.txt
cat days.txt | perl -p -e 's/\s+$/ /g'

The above regex approach is actually much simpler and neater! :D
sed — remove new line characters with sed

You could also use sed to remove new lines. The solution using sed is not very readable but it works. Use either of the following commands.
sed ':a;N;$!ba;s/\n//g' days.txt
cat days.txt | sed ':a;N;$!ba;s/\n//g'

Or, to replace the new line characters with spaces use either of the following commands.
sed ':a;N;$!ba;s/\n/ /g' days.txt
cat days.txt | sed ':a;N;$!ba;s/\n/ /g'

James of crypto.dsplabs.com.au suggested this, easier to read, sed solution on the Linux Blog Forums:
sed '{:q;N;s/\n//g;t q}' days.txt

C or C++ — remove new line characters with a C or C++ based binary
If you fancy none of the above approaches then create your own binary tool for this task using for example C or C++. Here is an example C source code: rmnl.c also courtesy of James.

#include <stdio.h>
int main(int argc, char *argv[]) {
    char k;
    while((k = getchar()) != EOF)
        if(k != 0x0D && k != 0x0A) putchar(k);
//        else putchar(' '); // replace newlines with spaces
    putchar(0x0A);
    return 0;
}

While my attempt at writing a new line removal tool in C++, rmnl.cpp, is listed below.
#include <iostream>
using namespace std;
 int main() {
    string line;
    while( getline(cin, line) && !cin.eof() ) cout << line; // delete newlines
//  while( getline(cin, line) && !cin.eof() ) cout << line << ' '; // replace n with spaces
    cout << endl;
    return 0;
}

Another way in C++ is to use stream iterators like so:
#include <iostream>
#include <iterator>
 int main () {
    std::remove_copy( std::istream_iterator<char>( std::cin ),
                      std::istream_iterator<char>(),
                      std::ostream_iterator<char>( std::cout ),
                      '\n' );
}

To compile the above sources with GNU gcc or g++ compiler use the following commands, respectively.
gcc rmnl.c -o rmnl
g++ rmnl.cpp -o rmnl

Either of the following commands can be used to run the newly created rmnl binary assuming that rmnl is in your path.
cat days.txt | rmnl
rmnl < days.txt

If rmnl binary in not in your path variable, but it is in your current directory, then replace rmnl above with ./rmnl like so:
cat days.txt | ./rmnl
./rmnl < days.txt

Here is the compiled binary: rmnl and some information about it:
$>file rmnl
        rmnl: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV),
              dynamically linked (uses shared libs), for GNU/Linux 2.6.9, not stripped
$>ldd rmnl
        linux-gate.so.1 =>  (0x0041d000)
        libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x00b21000)
        libm.so.6 => /lib/libm.so.6 (0x0086c000)
        libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x009ec000)
        libc.so.6 => /lib/libc.so.6 (0x0072a000)
        /lib/ld-linux.so.2 (0x0070d000)

Other approaches for removal of new line characters
The following are thanks to reddit.com readers.
Replacing new lines with spaces using xargs:

xargs echo < days.txt
cat days.txt | xargs echo
cat days.txt | xargs echo -n

Removing new lines using Haskell, f.e. with the Glasgow Haskell Compiler, ghci:
cat days.txt | ghci -e "interact (concat . lines)"

Removing new lines or substituting them with spaces using sam text editor:
printf ", x/.*/nq" | sam -d days.txt 2>/dev/null
(echo ', x/\n/ c/ /'; echo ', p'; echo q) | sam -d days.txt 2>/dev/null

Or its stream version ssam:
ssam -n ', x/.*/ p' < days.txt 2>/dev/null
ssam ', x/\n/ c/ /' < days.txt 2>/dev/null

Another approach is to use GNU Bash like so:
while read; do echo -n "$REPLY "; done < days.txt

Or even simpler:
echo -n `cat days.txt`
Or, Python like this:

python -c 'import sys; print sys.stdin.read().replace("\n", " ")' < days.txt