column


bash: Simple way to get n-th column

Using cut you can select any column and define a custom delimiter to support multiple input formats you can select a column (or more) with barely minimum code.

cut -d',' -f2 myFile.csv

The above command will read the file myFile.csv (which is a CSV file) break it down to columns using the ‘,‘ character and then get the second column.

The option -f specifies which field (column) you want to extract, and the option -d specifies what is the field delimiter (column) that is used in the input file.

The -f parameter allows you to select multiple columns at the same time. You can achieve that by defining multiple columns separated using the ‘,‘ and by defining ranges using the - character.

Examples

  • -f1 selects the first column
  • -f1,3,4 selects columns 1, 3 and 4
  • -f1-4 selects all columns in the range 1-4
  • -f1,3,5-7,9 selects columns 1,3,8 and all the columns in the range 5-7

Use awk to print the last N columns of a file or a pipe

In this post we will describe a way to print the last N number of columns in awk.

We will use this code as example, where we will print the last 2 columns only:

awk '{n = 2; for (--n; n >= 0; n--){ printf "%s\t",$(NF-n)} print ""}';
'

In the awk script we use the variable n to control how many columns we want to print. In the above example we initialized it  to the value 2 as that is the number of columns we want printed.

After, we use a for loop to iterate over the fields (in this case the last two fields) and we print them to the screen using printf "%s\t",$(NF-n) to avoid printing the new line character and to separate them with a tab character.

NF is a special variable in awk that holds the total number of fields available on that line. If you do not change the delimiter, then it will hold the number of words on the line.

$(NF-n) is the way we ask awk to gives us the variable value that is n places before the last.

Outside the loop we print "" to print the new line character between input rows.

Examples:

If we want to print the last two columns of the ls -l command we can do it as follows:

ls -l | awk '{i = 2; for (--i; i >= 0; i--){ printf "%s\t",$(NF-i)} print ""}';

If we want to print the last two columns of the /etc/passwd file we can do it as follows:

awk -F ':' '{i = 2; for (--i; i >= 0; i--){ printf "%s\t",$(NF-i)} print ""}' /etc/passwd;

Note that we change the delimiter with the command line argument -F ":"


Create a sortable ‘Modified Date’ sortable column for posts and pages in wordpress admin area 6

2016-07-14: Post updated to support both pages and posts without redundant/useless code

Paste the following in the functions.php file of your theme:

// Register the column for modified date
function bf_post_modified_column_register( $columns ) {
    $columns['post_modified'] = __( 'Modified Date', 'mytextdomain' );
    return $columns;
}
add_filter( 'manage_edit-post_columns', 'bf_post_modified_column_register' );
add_filter( 'manage_edit-page_columns', 'bf_post_modified_column_register' );

// Display the modified date column content
function bf_post_modified_column_display( $column_name, $post_id ) {
    if ( 'post_modified' != $column_name ){
        return;
    }
    $post_modified = get_post_field('post_modified', $post_id);
    if ( !$post_modified ){
        $post_modified = '' . __( 'undefined', 'mytextdomain' ) . '';
    }
    echo $post_modified;
}
add_action( 'manage_posts_custom_column', 'bf_post_modified_column_display', 10, 2 );
add_action( 'manage_pages_custom_column', 'bf_post_modified_column_display', 10, 2 );

// Register the modified date column as sortable
function bf_post_modified_column_register_sortable( $columns ) {
    $columns['post_modified'] = 'post_modified';
    return $columns;
}
add_filter( 'manage_edit-post_sortable_columns', 'bf_post_modified_column_register_sortable' );
add_filter( 'manage_edit-page_sortable_columns', 'bf_post_modified_column_register_sortable' );

When you refresh http://<Your Domain>/wp-admin/edit.php or http://<Your Domain>/wp-admin/edit.php?post_type=page the ‘Modified Date’ column will be visible and sortable.