SYmbolic LinK (SYLK)


Symbolic Link is a Microsoft file format typically used to exchange data between applications, specifically spreadsheets. SYLK files conventionally have a .slk suffix. Composed of only displayable ANSI characters, it can be easily created and processed by other applications, such as databases.
Microsoft does not publish a SYLK specification. Variants of the format are supported by Multiplan, Microsoft Excel, Microsoft Works, OpenOffice.org, and Gnumeric. The format was introduced in the 1980s and has not evolved since 1986.
A commonly encountered 'occurrence' of the SYLK file happens when a comma-separated value format is saved with an unquoted first field name of 'ID', that is the first two characters match the first two characters of the SYLK file format. Microsoft Excel will then emit misleading error messages relating to the format of the file, such as "The file you are trying to open, 'x.csv', is in a different format than specified by the file extension...".
SYLK is known to cause security issues, as it allows an attacker to run arbitrary code, offers the opportunity to disguise the attack vector under the benign-looking appearance of a CSV file, and is still enabled by default on recent versions of Microsoft Excel.

Limitations

SYLK does not have support for Unicode. Even if a SYLK file is created by an application that supports Unicode, the SYLK file will be encoded in the current system's ANSI code page, not in Unicode. If the application contained characters that were displayable in Unicode but have no code point in the current system's code page, they will be converted to question marks in the SYLK file.
The semicolon is treated as a field separator in SYLK, so cannot be used unescaped in data values. If a character string in the SYLK file is to contain a semicolon then it should be prefixed with another semicolon so the string would appear as e.g., "WIDGET;;AXC1254". MS Excel will strip the first semicolon on import and the data element will appear as "WIDGET;AXC1254".
Each line of a SYLK input file must be no longer than 260 characters. Otherwise, Microsoft Excel will issue an error message and skip loading the overlong line.

Sample SYLK code

As an example, the following SYLK code in a text file with the.slk extension:
ID;P
C;Y1;X1;K"Row 1"
C;Y2;X1;K"Row 2"
C;Y3;X1;K"Total"
C;Y1;X2;K11
C;Y2;X2;K22
C;Y3;X2;K33
E
would be displayed like this when read by an appropriate spreadsheet:

for numeric formatting

The formatting of 2 decimal digits is applied to Column 2 using 
F;P2;C2

where P0 is for General, P1 is for no decimal, P2 is for 2 digits, P3 has leading $ sign with 2 decimal points as defined below.
ID;P
P;PGeneral
P;P_;;_;;_;;_
P;P_;;_;;_;;_
P;P_;;_;;_;;_
C;Y1;X1;K"Row 1"
C;Y2;X1;K"Row 2"
C;Y3;X1;K"Total"
C;Y1;X2;K11
C;Y2;X2;K22
C;Y3;X2;K0;ER1C2+R2C2
F;P2;C2
E
would be displayed like this when read by an appropriate spreadsheet:

for column width

defines the widths of a group of columns:
; : one space
;< n1 > : the first column
;< n2 > : the last column
;< n3 > : the width of columns in number of characters
For example: Adding these SYLK codes will adjust the column width of column 1 and 2 to 20 and 30 respectively.

F;W1 1 20
F;W2 2 30

cell formatting properties

F; < cl > < n > < c2 >
; < cl > : one of the following 1-character formatting codes:
;< n > : the number of digits.
;< c2 > : one of the following 1-character alignment codes:
For example: The following SYLK code demonstrates the cell formatting properties:

 ID;P
 P;PGeneral
 C;Y1;X1;K"Row 1 Left Justify"
 F;P0;FG0L
 C;Y2;X1;K"Row 2 Right Justify"
 F;P0;FG0R
 C;Y3;X1;K"Total at Center"
 F;P0;FG0C
 C;Y1;X2;K11
 C;Y2;X2;K22
 C;Y3;X2;K0;ER1C2+R2C2
 F;Y1;X2;FF2L
 F;Y2;X2;FF2R
 F;Y3;X2;F$2C
 F;W1 2 25
 E

SYLK syntax


SYLK_file ::=
 Record +
Record ::=
 RecordType Field* newline

Date and time are stored as a floating point value. The whole number part is a number of days from the Jan 1 1900, the fraction is the number of seconds divided by 86400. Conversion to unix time can be done by subtracting the difference between Jan 1 1970 and Jan 1 1900 and then multiplying by 86400; converting from unix time to SYLK datetime is done by dividing the value by 86400 and then adding 25569. The cell style has to be set to some date formatting value, e.g. to be displayed properly.
.slk file exports opened with Excel have a limit of 255 characters in a cell. This limit is not present in LibreOffice.