Ημερήσια αρχεία: 15 Απριλίου 2016

Grep: Print only the words of the line that matched the regular expression, one per line

 στο Bash / GNU/Linux  επισημασμένο με ετικέτα grep / word Από 
grep -oh "\w*$YOUR_PATTERN\w*" *

We used the following parameters on our command:

-h, –no-filename : Suppress the prefixing of file names on output. This is the default when there is only  one  file  (or only standard input) to search.
-o, –only-matching : Print  only  the matched (non-empty) parts of a matching line,  with each such part on a separate output line.

Also, we wrapped out pattern with the \w* that matches  all word-constituent characters on either side. The * character states that it should find 0 or more of those characters in the pattern to match.

Bash: Determine state of file

 στο Bash / GNU/Linux  επισημασμένο με ετικέτα bash / executable / exist / file / folder / not empty / readable / writable Από

Following you will find some tests one can perform on a file to identify its state

Check if file $FILE does not exist

if [ ! -f "$FILE" ]; then
    echo "File $FILE does not exist";
fi

Check if file $FILE exists and is a directory

if [ -d "$FILE" ]; then
    echo "File $FILE exists and is a directory";
fi

Check if file $FILE exists and is a regular file (not a directory)

if [ -f "$FILE" ]; then
    echo "File $FILE exists and is a regular file (not a directory)";
fi

Check if file $FILE exists, we do not know what type it is (if it is a directory, socket, node, etc.)

if [ -e "$FILE" ]; then
    echo "File $FILE exists, we do not know what type it is (if it is a directory, socket, node, etc.)";
fi

Check if file $FILE exists and is a symbolic link

if [ -L "$FILE" ]; then
    echo "File $FILE exists and is a symbolic link";
fi

Check if file $FILE exists and is a socket

if [ -S "$FILE" ]; then
    echo "File $FILE exists and is a socket";
fi

Check if file $FILE exists and is not empty

if [ -s "$FILE" ]; then
    echo "File $FILE exists and is not empty";
fi

Check if file $FILE exists and is readable

if [ -r "$FILE" ]; then
    echo "File $FILE exists and is readable";
fi

Check if file $FILE exists and is writable

if [ -w "$FILE" ]; then
    echo "File $FILE exists and is writable";
fi

Check if file $FILE exists and is executable

if [ -x "$FILE" ]; then
    echo "File $FILE exists and is executable";
fi

Bash: How to iterate over associative array and print all key/value pairs

 στο Bash / GNU/Linux  επισημασμένο με ετικέτα associative array / bash / iterate Από

The values of an associative array are accessed using the following syntax ${ARRAY[@]}.

To access the keys of an associative array in bash you need to use  an exclamation point right before the name of the array: ${!ARRAY[@]}.

To iterate over the key/value pairs you can do something like the following example

# For every key in the associative array..
for KEY in "${!ARRAY[@]}"; do
  # Print the KEY value
  echo "Key: $KEY"
  # Print the VALUE attached to that KEY
  echo "Value: ${ARRAY[$KEY]}"
done

NOTE: The use of quotes around the array of keys ${!ARRAY[@]} in the for statement (plus the use of @ instead of *) is necessary in case any keys include spaces.

Bash: Grep lines that start with a tab character

 στο Bash / GNU/Linux  επισημασμένο με ετικέτα perl / regular expression Από

Using a regular expression to match the lines that start with a tab we wrote the following

grep -P '^\t'

The -P parameter (or –perl-regexp) directs grep to interpret the pattern as a Perl regular expression.

The ^ character directs the pattern to match the start of the line.
The \t character directs the pattern to match a tab character.