## VIPS from the command-line

Using VIPS — How to use the VIPS library from the command-line

#### Introduction

Use the vips command to execute VIPS operations from the command-line. For example:

    $ vips rot k2.jpg x.jpg d90

Will rotate the image `k2.jpg` by 90 degrees anticlockwise and write the result to the file `x.jpg`. If you don't give any arguments to an operation, vips will give a short description, for example:

    $ vips rot
    rotate an image
    usage:
       rot in out angle
    where:
       in           - Input image, input VipsImage
       out          - Output image, output VipsImage
       angle        - Angle to rotate image, input VipsAngle
                            default: d90
                            allowed: d0, d90, d180, d270

There's a straightforward relationship with the C API: compare this to the API docs for `vips_rot()`.

#### Listing all operations

You can list all classes with:

    $ vips -l
    ...
    VipsOperation (operation), operations
      VipsSystem (system), run an external command
      VipsArithmetic (arithmetic), arithmetic operations
        VipsBinary (binary), binary operations
          VipsAdd (add), add two images
          ... etc.

Each line shows the canonical name of the class (for example `VipsAdd`), the class nickname (`add` in this case), and a short description. Some subclasses of operation will show more: for example, subclasses of `VipsForeign` will show some of the extra flags supported by the file load/save operations.

The API docs have a handy table of all vips operations, if you want to find out how to do something, try searching that.

#### Optional arguments

Many operations take optional arguments. You can supply these as command-line options. For example:

    $ vips gamma
    gamma an image
    usage:
       gamma in out
    where:
       in           - Input image, input VipsImage
       out          - Output image, output VipsImage
    optional arguments:
       exponent     - Gamma factor, input gdouble
                      default: 2.4
                      min: 1e-06, max: 1000
    operation flags: sequential-unbuffered

`vips_gamma()` applies a gamma factor to an image. By default, it uses 2.4, the sRGB gamma factor, but you can specify any gamma with the `exponent` option.

Use it from the command-line like this:

    $ vips gamma k2.jpg x.jpg --exponent 0.42

This will read file `k2.jpg`, un-gamma it, and write the result to file `x.jpg`.

#### Array arguments

Some operations take arrays of values as arguments. For example, `vips_affine()` needs an array of four numbers for the 2x2 transform matrix. You pass arrays as space-separated lists:

    $ vips affine k2.jpg x.jpg "2 0 0 1"

You may need the quotes to stop your shell breaking the argument at the spaces. `vips_bandjoin()` needs an array of input images to join, run it like this:

    $ vips bandjoin "k2.jpg k4.jpg" x.tif

#### Implicit file format conversion

vips will automatically convert between image file formats for you. Input images are detected by sniffing their first few bytes; output formats are set from the filename suffix. You can see a list of all the supported file formats with something like:

    $ vips -l foreign

Then get a list of the options a format supports with:

    $ vips jpegsave

You can pass options to the implicit load and save operations enclosed in square brackets after the filename:

    vips affine k2.jpg x.jpg[Q=90,strip] "2 0 0 1"

Will write `x.jpg` at quality level 90 and will strip all metadata from the image.

#### Chaining operations

Because each operation runs in a separate process, you can't use libvips's chaining system to join operations together, you have to use intermediate files. The command-line interface is therefore quite a bit slower than Python or C.

The best alternative is to use vips files for intermediates. Something like:

    vips invert input.jpg t1.v
    vips affine t1.v output.jpg "2 0 0 1"
    rm t1.v

#### Other features

Finally, vips has a couple of useful extra options.

- Use `--vips-progress` to get vips to display a simple progress indicator.

- Use `--vips-leak` and vips will leak-test on exit, and also display an estimate of peak memory use.

- Set `G_MESSAGES_DEBUG=VIPS` and GLib will display informational and debug messages from libvips.

VIPS comes with a couple of other useful programs. vipsheader is a command which can print image header fields. vipsedit can change fields in vips format images. vipsthumbnail can make image thumbnails quickly.